Chapter 17. APIs and Libraries

Table of Contents

17.1. libmysqld, the Embedded MySQL Server Library
17.1.1. Compiling Programs with libmysqld
17.1.2. Restrictions When Using the Embedded MySQL Server
17.1.3. Options with the Embedded Server
17.1.4. Embedded Server Examples
17.1.5. Licensing the Embedded Server
17.2. MySQL C API
17.2.1. C API Data Types
17.2.2. C API Function Overview
17.2.3. C API Function Descriptions
17.2.4. C API Prepared Statements
17.2.5. C API Prepared Statement Data types
17.2.6. C API Prepared Statement Function Overview
17.2.7. C API Prepared Statement Function Descriptions
17.2.8. C API Prepared Statement Problems
17.2.9. C API Handling of Multiple Statement Execution
17.2.10. C API Handling of Date and Time Values
17.2.11. C API Threaded Function Descriptions
17.2.12. C API Embedded Server Function Descriptions
17.2.13. Controlling Automatic Reconnect Behavior
17.2.14. Common Questions and Problems When Using the C API
17.2.15. Building Client Programs
17.2.16. How to Make a Threaded Client
17.3. MySQL PHP API
17.3.1. Common Problems with MySQL and PHP
17.3.2. Enabling Both mysql and mysqli in PHP
17.4. MySQL Perl API
17.5. MySQL C++ API
17.6. MySQL Python API
17.7. MySQL Tcl API
17.8. MySQL Eiffel Wrapper

This chapter describes the APIs available for MySQL, where to get them, and how to use them. The C API is the most extensively covered, because it was developed by the MySQL team, and is the basis for most of the other APIs. This chapter also covers the libmysqld library (the embedded server).

17.1. libmysqld, the Embedded MySQL Server Library

The embedded MySQL server library makes it possible to run a full-featured MySQL server inside a client application. The main benefits are increased speed and more simple management for embedded applications.

The embedded server library is based on the client/server version of MySQL, which is written in C/C++. Consequently, the embedded server also is written in C/C++. There is no embedded server available in other languages.

The API is identical for the embedded MySQL version and the client/server version. To change an old threaded application to use the embedded library, you normally only have to add calls to the following functions:

FunctionWhen to Call
mysql_library_init()Should be called before any other MySQL function is called, preferably early in the main() function.
mysql_library_end()Should be called before your program exits.
mysql_thread_init()Should be called in each thread you create that accesses MySQL.
mysql_thread_end()Should be called before calling pthread_exit()

Then you must link your code with libmysqld.a instead of libmysqlclient.a. To ensure binary compatibility between your application and the server library, be sure to compile your application against headers for the same series of MySQL that was used to compile the server library. For example, if libmysqld was compiled against MySQL 4.1 headers, do not compile your application against MySQL 5.1 headers, or vice versa.

The mysql_library_xxx() functions are also included in libmysqlclient.a to allow you to change between the embedded and the client/server version by just linking your application with the right library. See Section 17.2.3.38, “mysql_library_init().

One difference between the embedded server and the standalone server is that for the embedded server, authentication for connections is disabled by default. To use authentication for the embedded server, specify the --with-embedded-privilege-control option when you invoke configure to configure your MySQL distribution. This option is available as of MySQL 4.1.3.

17.1.1. Compiling Programs with libmysqld

In precompiled binary MySQL distributions that include libmysqld, the embedded server library, MySQL builds the library using the appropriate vendor compiler if there is one.

To get a libmysqld library if you build MySQL from source yourself, you should configure MySQL with the --with-embedded-server option. See Section 2.9.2, “Typical configure Options”.

When you link your program with libmysqld, you must also include the system-specific pthread libraries and some libraries that the MySQL server uses. You can get the full list of libraries by executing mysql_config --libmysqld-libs.

The correct flags for compiling and linking a threaded program must be used, even if you do not directly call any thread functions in your code.

To compile a C program to include the necessary files to embed the MySQL server library into an executable version of a program, the compiler will need to know where to find various files and need instructions on how to compile the program. The following example shows how a program could be compiled from the command line, assuming that you are using gcc, use the GNU C compiler:

gcc mysql_test.c -o mysql_test -lz \
`/usr/local/mysql/bin/mysql_config --include --libmysqld-libs`

Immediately following the gcc command is the name of the C program source file. After it, the -o option is given to indicate that the file name that follows is the name that the compiler is to give to the output file, the compiled program. The next line of code tells the compiler to obtain the location of the include files and libraries and other settings for the system on which it's compiled. Because of a problem with mysql_config, the option -lz (for compression) is added here. The mysql_config command is contained in backticks, not single quotes.

On some non-gcc platforms, the embedded library depends on C++ runtime libraries and linking against the embedded library might result in missing-symbol errors. To solve this, link using a C++ compiler or explicitly list the required libraries on the link command line.

17.1.2. Restrictions When Using the Embedded MySQL Server

The embedded server has the following limitations:

  • No support for ISAM tables. (This is done mainly to make the library smaller.)

  • No user-defined functions (UDFs).

  • No stack trace on core dump.

  • No internal RAID support. (This is not normally needed as most current operating systems support big files.)

  • You cannot set this up as a master or a slave (no replication).

  • Very large result sets may be unusable on low memory systems.

  • You cannot connect to an embedded server from an outside process with sockets or TCP/IP. However, you can connect to an intermediate application, which in turn can connect to an embedded server on the behalf of a remote client or outside process.

  • InnoDB is not reentrant in the embedded server and cannot be used for multiple connections, either successively or simultaneously.

Some of these limitations can be changed by editing the mysql_embed.h include file and recompiling MySQL.

17.1.3. Options with the Embedded Server

Any options that may be given with the mysqld server daemon, may be used with an embedded server library. Server options may be given in an array as an argument to the mysql_library_init(), which initializes the server. They also may be given in an option file like my.cnf. To specify an option file for a C program, use the --defaults-file option as one of the elements of the second argument of the mysql_library_init() function. See Section 17.2.3.38, “mysql_library_init(), for more information on the mysql_library_init() function.

Using option files can make it easier to switch between a client/server application and one where MySQL is embedded. Put common options under the [server] group. These are read by both MySQL versions. Client/server-specific options should go under the [mysqld] section. Put options specific to the embedded MySQL server library in the [embedded] section. Options specific to applications go under section labeled [ApplicationName_SERVER]. See Section 4.2.3.2, “Using Option Files”.

17.1.4. Embedded Server Examples

These two example programs should work without any changes on a Linux or FreeBSD system. For other operating systems, minor changes are needed, mostly with file paths. These examples are designed to give enough details for you to understand the problem, without the clutter that is a necessary part of a real application. The first example is very straightforward. The second example is a little more advanced with some error checking. The first is followed by a command-line entry for compiling the program. The second is followed by a GNUmake file that may be used for compiling instead.

Example 1

test1_libmysqld.c

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include "mysql.h"

MYSQL *mysql;
MYSQL_RES *results;
MYSQL_ROW record;

static char *server_options[] = { "mysql_test", "--defaults-file=my.cnf", NULL };
int num_elements = (sizeof(server_options) / sizeof(char *)) - 1;

static char *server_groups[] = { "libmysqld_server", "libmysqld_client", NULL };

int main(void)
{
   mysql_library_init(num_elements, server_options, server_groups);
   mysql = mysql_init(NULL);
   mysql_options(mysql, MYSQL_READ_DEFAULT_GROUP, "libmysqld_client");
   mysql_options(mysql, MYSQL_OPT_USE_EMBEDDED_CONNECTION, NULL);

   mysql_real_connect(mysql, NULL,NULL,NULL, "database1", 0,NULL,0);

   mysql_query(mysql, "SELECT column1, column2 FROM table1");

   results = mysql_store_result(mysql);

   while((record = mysql_fetch_row(results))) {
      printf("%s - %s \n", record[0], record[1]);
   }

   mysql_free_result(results);
   mysql_close(mysql);
   mysql_library_end();

   return 0;
}

Here is the command line for compiling the above program:

gcc test1_libmysqld.c -o test1_libmysqld -lz \
 `/usr/local/mysql/bin/mysql_config --include --libmysqld-libs`

Example 2

To try out the example, create a test2_libmysqld directory at the same level as the MySQL source directory. Save the test2_libmysqld.c source and the GNUmakefile in the directory, and run GNU make from inside the test2_libmysqld directory.

test2_libmysqld.c

/*
 * A simple example client, using the embedded MySQL server library
*/

#include <mysql.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

MYSQL *db_connect(const char *dbname);
void db_disconnect(MYSQL *db);
void db_do_query(MYSQL *db, const char *query);

const char *server_groups[] = {
  "test2_libmysqld_SERVER", "embedded", "server", NULL
};

int
main(int argc, char **argv)
{
  MYSQL *one, *two;

  /* mysql_library_init() must be called before any other mysql
   * functions.
   *
   * You can use mysql_library_init(0, NULL, NULL), and it
   * initializes the server using groups = {
   *   "server", "embedded", NULL
   *  }.
   *
   * In your $HOME/.my.cnf file, you probably want to put:

[test2_libmysqld_SERVER]
language = /path/to/source/of/mysql/sql/share/english

   * You could, of course, modify argc and argv before passing
   * them to this function.  Or you could create new ones in any
   * way you like.  But all of the arguments in argv (except for
   * argv[0], which is the program name) should be valid options
   * for the MySQL server.
   *
   * If you link this client against the normal mysqlclient
   * library, this function is just a stub that does nothing.
   */
  mysql_library_init(argc, argv, (char **)server_groups);

  one = db_connect("test");
  two = db_connect(NULL);

  db_do_query(one, "SHOW TABLE STATUS");
  db_do_query(two, "SHOW DATABASES");

  mysql_close(two);
  mysql_close(one);

  /* This must be called after all other mysql functions */
  mysql_library_end();

  exit(EXIT_SUCCESS);
}

static void
die(MYSQL *db, char *fmt, ...)
{
  va_list ap;
  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  va_end(ap);
  (void)putc('\n', stderr);
  if (db)
    db_disconnect(db);
  exit(EXIT_FAILURE);
}

MYSQL *
db_connect(const char *dbname)
{
  MYSQL *db = mysql_init(NULL);
  if (!db)
    die(db, "mysql_init failed: no memory");
  /*
   * Notice that the client and server use separate group names.
   * This is critical, because the server does not accept the
   * client's options, and vice versa.
   */
  mysql_options(db, MYSQL_READ_DEFAULT_GROUP, "test2_libmysqld_CLIENT");
  if (!mysql_real_connect(db, NULL, NULL, NULL, dbname, 0, NULL, 0))
    die(db, "mysql_real_connect failed: %s", mysql_error(db));

  return db;
}

void
db_disconnect(MYSQL *db)
{
  mysql_close(db);
}

void
db_do_query(MYSQL *db, const char *query)
{
  if (mysql_query(db, query) != 0)
    goto err;

  if (mysql_field_count(db) > 0)
  {
    MYSQL_RES   *res;
    MYSQL_ROW    row, end_row;
    int num_fields;

    if (!(res = mysql_store_result(db)))
      goto err;
    num_fields = mysql_num_fields(res);
    while ((row = mysql_fetch_row(res)))
    {
      (void)fputs(">> ", stdout);
      for (end_row = row + num_fields; row < end_row; ++row)
        (void)printf("%s\t", row ? (char*)*row : "NULL");
      (void)fputc('\n', stdout);
    }
    (void)fputc('\n', stdout);
    mysql_free_result(res);
  }
  else
    (void)printf("Affected rows: %lld\n", mysql_affected_rows(db));

  return;

err:
  die(db, "db_do_query failed: %s [%s]", mysql_error(db), query);
}

GNUmakefile

# This assumes the MySQL software is installed in /usr/local/mysql
inc      := /usr/local/mysql/include/mysql
lib      := /usr/local/mysql/lib

# If you have not installed the MySQL software yet, try this instead
#inc      := $(HOME)/mysql-4.0/include
#lib      := $(HOME)/mysql-4.0/libmysqld

CC       := gcc
CPPFLAGS := -I$(inc) -D_THREAD_SAFE -D_REENTRANT
CFLAGS   := -g -W -Wall
LDFLAGS  := -static
# You can change -lmysqld to -lmysqlclient to use the
# client/server library
LDLIBS    = -L$(lib) -lmysqld -lz -lm -ldl -lcrypt

ifneq (,$(shell grep FreeBSD /COPYRIGHT 2>/dev/null))
# FreeBSD
LDFLAGS += -pthread
else
# Assume Linux
LDLIBS += -lpthread
endif

# This works for simple one-file test programs
sources := $(wildcard *.c)
objects := $(patsubst %c,%o,$(sources))
targets := $(basename $(sources))

all: $(targets)

clean:
        rm -f $(targets) $(objects) *.core

17.1.5. Licensing the Embedded Server

We encourage everyone to promote free software by releasing code under the GPL or a compatible license. For those who are not able to do this, another option is to purchase a commercial license for the MySQL code from MySQL AB. For details, please see http://www.mysql.com/company/legal/licensing/.

17.2. MySQL C API

The C API code is distributed with MySQL. It is included in the mysqlclient library and allows C programs to access a database.

Many of the clients in the MySQL source distribution are written in C. If you are looking for examples that demonstrate how to use the C API, take a look at these clients. You can find these in the clients directory in the MySQL source distribution.

Most of the other client APIs (all except Connector/J and Connector/NET) use the mysqlclient library to communicate with the MySQL server. This means that, for example, you can take advantage of many of the same environment variables that are used by other client programs, because they are referenced from the library. See Chapter 4, MySQL Programs, for a list of these variables.

The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16KB) is automatically increased up to the maximum size (the maximum is 16MB). Because buffer sizes are increased only as demand warrants, simply increasing the default maximum limit does not in itself cause more resources to be used. This size check is mostly a check for erroneous statements and communication packets.

The communication buffer must be large enough to contain a single SQL statement (for client-to-server traffic) and one row of returned data (for server-to-client traffic). Each thread's communication buffer is dynamically enlarged to handle any query or row up to the maximum limit. For example, if you have BLOB values that contain up to 16MB of data, you must have a communication buffer limit of at least 16MB (in both server and client). The client's default maximum is 16MB, but the default maximum in the server is 1MB. You can increase this by changing the value of the max_allowed_packet parameter when the server is started. See Section 7.5.2, “Tuning Server Parameters”.

The MySQL server shrinks each communication buffer to net_buffer_length bytes after each query. For clients, the size of the buffer associated with a connection is not decreased until the connection is closed, at which time client memory is reclaimed.

For programming with threads, see Section 17.2.16, “How to Make a Threaded Client”. For creating a standalone application which includes the "server" and "client" in the same program (and does not communicate with an external MySQL server), see Section 17.1, “libmysqld, the Embedded MySQL Server Library”.

MySQL Enterprise MySQL Enterprise subscribers will find more information about using the C API in the Knowledge Base articles, The C API. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

17.2.1. C API Data Types

This section describes C API data types other than those used for prepared statements. For information about the latter, see Section 17.2.5, “C API Prepared Statement Data types”.

  • MYSQL

    This structure represents a handle to one database connection. It is used for almost all MySQL functions. You should not try to make a copy of a MYSQL structure. There is no guarantee that such a copy will be usable.

  • MYSQL_RES

    This structure represents the result of a query that returns rows (SELECT, SHOW, DESCRIBE, EXPLAIN). The information returned from a query is called the result set in the remainder of this section.

  • MYSQL_ROW

    This is a type-safe representation of one row of data. It is currently implemented as an array of counted byte strings. (You cannot treat these as null-terminated strings if field values may contain binary data, because such values may contain null bytes internally.) Rows are obtained by calling mysql_fetch_row().

  • MYSQL_FIELD

    This structure contains information about a field, such as the field's name, type, and size. Its members are described in more detail here. You may obtain the MYSQL_FIELD structures for each field by calling mysql_fetch_field() repeatedly. Field values are not part of this structure; they are contained in a MYSQL_ROW structure.

  • MYSQL_FIELD_OFFSET

    This is a type-safe representation of an offset into a MySQL field list. (Used by mysql_field_seek().) Offsets are field numbers within a row, beginning at zero.

  • my_ulonglong

    The type used for the number of rows and for mysql_affected_rows(), mysql_num_rows(), and mysql_insert_id(). This type provides a range of 0 to 1.84e19.

    On some systems, attempting to print a value of type my_ulonglong does not work. To print such a value, convert it to unsigned long and use a %lu print format. Example:

    printf ("Number of rows: %lu\n", 
            (unsigned long) mysql_num_rows(result));
    
  • my_bool

    A boolean type, for values that are true (non-zero) or false (zero).

The MYSQL_FIELD structure contains the members listed here:

  • char * name

    The name of the field, as a null-terminated string. If the field was given an alias with an AS clause, the value of name is the alias.

  • char * org_name

    The name of the field, as a null-terminated string. Aliases are ignored. This member was added in MySQL 4.1.0.

  • char * table

    The name of the table containing this field, if it isn't a calculated field. For calculated fields, the table value is an empty string. If the table was given an alias with an AS clause, the value of table is the alias. For a UNION, the value is the empty string as of MySQL 4.0.26.

  • char * org_table

    The name of the table, as a null-terminated string. Aliases are ignored. For a UNION, the value is the empty string as of MySQL 4.0.26. This member was added in MySQL 4.1.0.

  • char * db

    The name of the database that the field comes from, as a null-terminated string. If the field is a calculated field, db is an empty string. For a UNION, the value is the empty string as of MySQL 4.0.26. This member was added in MySQL 4.1.0.

  • char * catalog

    The catalog name. This value is always "def". This member was added in MySQL 4.1.1.

  • char * def

    The default value of this field, as a null-terminated string. This is set only if you use mysql_list_fields().

  • unsigned long length

    The width of the field. This corresponds to the display length, in bytes.

  • unsigned long max_length

    The maximum width of the field for the result set (the length in bytes of the longest field value for the rows actually in the result set). If you use mysql_store_result() or mysql_list_fields(), this contains the maximum length for the field. If you use mysql_use_result(), the value of this variable is zero.

    The value of max_length is the length of the string representation of the values in the result set. For example, if you retrieve a FLOAT column and the “widest” value is -12.345, max_length is 7 (the length of '-12.345').

    If you are using prepared statements, max_length is not set by default because for the binary protocol the lengths of the values depend on the types of the values in the result set. (See Section 17.2.5, “C API Prepared Statement Data types”.) If you want the max_length values anyway, enable the STMT_ATTR_UPDATE_MAX_LENGTH option with mysql_stmt_attr_set() and the lengths will be set when you call mysql_stmt_store_result(). (See Section 17.2.7.3, “mysql_stmt_attr_set(), and Section 17.2.7.27, “mysql_stmt_store_result().)

  • unsigned int name_length

    The length of name. This member was added in MySQL 4.1.0.

  • unsigned int org_name_length

    The length of org_name. This member was added in MySQL 4.1.0.

  • unsigned int table_length

    The length of table. This member was added in MySQL 4.1.0.

  • unsigned int org_table_length

    The length of org_table. This member was added in MySQL 4.1.0.

  • unsigned int db_length

    The length of db. This member was added in MySQL 4.1.0.

  • unsigned int catalog_length

    The length of catalog. This member was added in MySQL 4.1.1.

  • unsigned int def_length

    The length of def. This member was added in MySQL 4.1.0.

  • unsigned int flags

    Different bit-flags for the field. The flags value may have zero or more of the following bits set:

    Flag ValueFlag Description
    NOT_NULL_FLAGField can't be NULL
    PRI_KEY_FLAGField is part of a primary key
    UNIQUE_KEY_FLAGField is part of a unique key
    MULTIPLE_KEY_FLAGField is part of a non-unique key
    UNSIGNED_FLAGField has the UNSIGNED attribute
    ZEROFILL_FLAGField has the ZEROFILL attribute
    BINARY_FLAGField has the BINARY attribute
    AUTO_INCREMENT_FLAGField has the AUTO_INCREMENT attribute
    ENUM_FLAGField is an ENUM (deprecated)
    SET_FLAGField is a SET (deprecated)
    BLOB_FLAGField is a BLOB or TEXT (deprecated)
    TIMESTAMP_FLAGField is a TIMESTAMP (deprecated)

    Use of the BLOB_FLAG, ENUM_FLAG, SET_FLAG, and TIMESTAMP_FLAG flags is deprecated because they indicate the type of a field rather than an attribute of its type. It is preferable to test field->type against MYSQL_TYPE_BLOB, MYSQL_TYPE_ENUM, MYSQL_TYPE_SET, or MYSQL_TYPE_TIMESTAMP instead.

    NUM_FLAG indicates that a column is numeric. This includes columns with a type of MYSQL_TYPE_DECIMAL, MYSQL_TYPE_TINY, MYSQL_TYPE_SHORT, MYSQL_TYPE_LONG, MYSQL_TYPE_FLOAT, MYSQL_TYPE_DOUBLE, MYSQL_TYPE_NULL, MYSQL_TYPE_TIMESTAMP, MYSQL_TYPE_LONGLONG, MYSQL_TYPE_INT24, and MYSQL_TYPE_YEAR.

    The following example illustrates a typical use of the flags value:

    if (field->flags & NOT_NULL_FLAG)
        printf("Field can't be null\n");
    

    You may use the following convenience macros to determine the boolean status of the flags value:

    Flag StatusDescription
    IS_NOT_NULL(flags)True if this field is defined as NOT NULL
    IS_PRI_KEY(flags)True if this field is a primary key
    IS_BLOB(flags)True if this field is a BLOB or TEXT (deprecated; test field->type instead)
  • unsigned int decimals

    The number of decimals for numeric fields.

  • unsigned int charsetnr

    An ID number that indicates the character set/collation pair for the field. This member was added in MySQL 4.1.0.

    To distinguish between binary and non-binary data for string data types, check whether the charsetnr value is 63. If so, the character set is binary, which indicates binary rather than non-binary data. This enables you to distinguish BINARY from CHAR, VARBINARY from VARCHAR, and the BLOB types from the TEXT types.

    charsetnr values are the same as those displayed in the Id column of the SHOW COLLATION statement. You can use this statement to see which character set and collation specific charsetnr values indicate:

    mysql> SHOW COLLATION;
    +----------------------+----------+-----+---------+----------+---------+
    | Collation            | Charset  | Id  | Default | Compiled | Sortlen |
    +----------------------+----------+-----+---------+----------+---------+
    ...
    | utf8_general_ci      | utf8     |  33 | Yes     | Yes      |       1 | 
    ...
    | binary               | binary   |  63 | Yes     | Yes      |       1 | 
    ...
    +----------------------+----------+-----+---------+----------+---------+
    
  • enum enum_field_types type

    The type of the field. The type value may be one of the MYSQL_TYPE_ symbols shown in the following table. Before MySQL 4.1, the symbol names begin with FIELD_TYPE_ rather than MYSQL_TYPE_. The older types still are recognized for backward compatibility.

    Type ValueType Description
    MYSQL_TYPE_TINYTINYINT field
    MYSQL_TYPE_SHORTSMALLINT field
    MYSQL_TYPE_LONGINTEGER field
    MYSQL_TYPE_INT24MEDIUMINT field
    MYSQL_TYPE_LONGLONGBIGINT field
    MYSQL_TYPE_DECIMALDECIMAL or NUMERIC field
    MYSQL_TYPE_FLOATFLOAT field
    MYSQL_TYPE_DOUBLEDOUBLE or REAL field
    MYSQL_TYPE_TIMESTAMPTIMESTAMP field
    MYSQL_TYPE_DATEDATE field
    MYSQL_TYPE_TIMETIME field
    MYSQL_TYPE_DATETIMEDATETIME field
    MYSQL_TYPE_YEARYEAR field
    MYSQL_TYPE_STRINGCHAR or BINARY field
    MYSQL_TYPE_VAR_STRINGVARCHAR or VARBINARY field
    MYSQL_TYPE_BLOBBLOB or TEXT field (use max_length to determine the maximum length)
    MYSQL_TYPE_SETSET field
    MYSQL_TYPE_ENUMENUM field
    MYSQL_TYPE_GEOMETRYSpatial field (MySQL 4.1.0 and up)
    MYSQL_TYPE_NULLNULL-type field

    You can use the IS_NUM() macro to test whether a field has a numeric type. Pass the type value to IS_NUM() and it evaluates to TRUE if the field is numeric:

    if (IS_NUM(field->type))
        printf("Field is numeric\n");
    

17.2.2. C API Function Overview

The functions available in the C API are summarized here and described in greater detail in a later section. See Section 17.2.3, “C API Function Descriptions”.

FunctionDescription
my_init()Initialize global variables, and thread handler in thread-safe programs
mysql_affected_rows()Returns the number of rows changed/deleted/inserted by the last UPDATE, DELETE, or INSERT query
mysql_autocommit()Toggles autocommit mode on/off
mysql_change_user()Changes user and database on an open connection
mysql_character_set_name()Return default character set name for current connection
mysql_close()Closes a server connection
mysql_commit()Commits the transaction
mysql_connect()Connects to a MySQL server (this function is deprecated; use mysql_real_connect() instead)
mysql_create_db()Creates a database (this function is deprecated; use the SQL statement CREATE DATABASE instead)
mysql_data_seek()Seeks to an arbitrary row number in a query result set
mysql_debug()Does a DBUG_PUSH with the given string
mysql_drop_db()Drops a database (this function is deprecated; use the SQL statement DROP DATABASE instead)
mysql_dump_debug_info()Makes the server write debug information to the log
mysql_eof()Determines whether the last row of a result set has been read (this function is deprecated; mysql_errno() or mysql_error() may be used instead)
mysql_errno()Returns the error number for the most recently invoked MySQL function
mysql_error()Returns the error message for the most recently invoked MySQL function
mysql_escape_string()Escapes special characters in a string for use in an SQL statement
mysql_fetch_field()Returns the type of the next table field
mysql_fetch_field_direct()Returns the type of a table field, given a field number
mysql_fetch_fields()Returns an array of all field structures
mysql_fetch_lengths()Returns the lengths of all columns in the current row
mysql_fetch_row()Fetches the next row from the result set
mysql_field_count()Returns the number of result columns for the most recent statement
mysql_field_seek()Puts the column cursor on a specified column
mysql_field_tell()Returns the position of the field cursor used for the last mysql_fetch_field()
mysql_free_result()Frees memory used by a result set
mysql_get_client_info()Returns client version information as a string
mysql_get_client_version()Returns client version information as an integer
mysql_get_host_info()Returns a string describing the connection
mysql_get_proto_info()Returns the protocol version used by the connection
mysql_get_server_info()Returns the server version number
mysql_get_server_version()Returns version number of server as an integer
mysql_hex_string()Encode string in hexadecimal format
mysql_info()Returns information about the most recently executed query
mysql_init()Gets or initializes a MYSQL structure
mysql_insert_id()Returns the ID generated for an AUTO_INCREMENT column by the previous query
mysql_kill()Kills a given thread
mysql_library_end()Finalize the MySQL C API library
mysql_library_init()Initialize the MySQL C API library
mysql_list_dbs()Returns database names matching a simple regular expression
mysql_list_fields()Returns field names matching a simple regular expression
mysql_list_processes()Returns a list of the current server threads
mysql_list_tables()Returns table names matching a simple regular expression
mysql_more_results()Checks whether any more results exist
mysql_next_result()Returns/initiates the next result in multiple-statement executions
mysql_num_fields()Returns the number of columns in a result set
mysql_num_rows()Returns the number of rows in a result set
mysql_options()Sets connect options for mysql_real_connect()
mysql_ping()Checks whether the connection to the server is working, reconnecting as necessary
mysql_query()Executes an SQL query specified as a null-terminated string
mysql_real_connect()Connects to a MySQL server
mysql_real_escape_string()Escapes special characters in a string for use in an SQL statement, taking into account the current character set of the connection
mysql_real_query()Executes an SQL query specified as a counted string
mysql_refresh()Flush or reset tables and caches
mysql_reload()Tells the server to reload the grant tables
mysql_rollback()Rolls back the transaction
mysql_row_seek()Seeks to a row offset in a result set, using value returned from mysql_row_tell()
mysql_row_tell()Returns the row cursor position
mysql_select_db()Selects a database
mysql_server_end()Finalize the MySQL C API library
mysql_server_init()Initialize the MySQL C API library
mysql_set_character_set()Set default character set for current connection
mysql_set_local_infile_default()Set the LOAD DATA LOCAL INFILE handler callbacks to their default values
mysql_set_local_infile_handler()Install application-specific LOAD DATA LOCAL INFILE handler callbacks
mysql_set_server_option()Sets an option for the connection (like multi-statements)
mysql_sqlstate()Returns the SQLSTATE error code for the last error
mysql_shutdown()Shuts down the database server
mysql_ssl_set()Prepare to establish SSL connection to server
mysql_stat()Returns the server status as a string
mysql_store_result()Retrieves a complete result set to the client
mysql_thread_end()Finalize thread handler
mysql_thread_id()Returns the current thread ID
mysql_thread_init()Initialize thread handler
mysql_thread_safe()Returns 1 if the clients are compiled as thread-safe
mysql_use_result()Initiates a row-by-row result set retrieval
mysql_warning_count()Returns the warning count for the previous SQL statement

Application programs should use this general outline for interacting with MySQL:

  1. Initialize the MySQL library by calling mysql_library_init(). This function exists in both the mysqlclient C client library and the mysqld embedded server library, so it is used whether you build a regular client program by linking with the -libmysqlclient flag, or an embedded server application by linking with the -libmysqld flag.

  2. Initialize a connection handler by calling mysql_init() and connect to the server by calling mysql_real_connect().

  3. Issue SQL statements and process their results. (The following discussion provides more information about how to do this.)

  4. Close the connection to the MySQL server by calling mysql_close().

  5. End use of the MySQL library by calling mysql_library_end().

The purpose of calling mysql_library_init() and mysql_library_end() is to provide proper initialization and finalization of the MySQL library. For applications that are linked with the client library, they provide improved memory management. If you don't call mysql_library_end(), a block of memory remains allocated. (This does not increase the amount of memory used by the application, but some memory leak detectors will complain about it.) For applications that are linked with the embedded server, these calls start and stop the server.

mysql_library_init() and mysql_library_end() are available as of MySQL 4.1.10. For older versions of MySQL, you can call mysql_server_init() and mysql_server_end() instead.

In a non-multi-threaded environment, the call to mysql_library_init() may be omitted, because mysql_init() will invoke it automatically as necessary. However, mysql_library_init() is not thread-safe in a multi-threaded environment, and thus neither is mysql_init(), which calls mysql_library_init(). You must either call mysql_library_init() prior to spawning any threads, or else use a mutex to protect the call, whether you invoke mysql_library_init() or indirectly via mysql_init(). This should be done prior to any other client library call.

To connect to the server, call mysql_init() to initialize a connection handler, then call mysql_real_connect() with that handler (along with other information such as the hostname, username, and password). Upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1. A value of 1 for this flag indicates that if a statement cannot be performed because of a lost connection, to try reconnecting to the server before giving up. When you are done with the connection, call mysql_close() to terminate it.

While a connection is active, the client may send SQL statements to the server using mysql_query() or mysql_real_query(). The difference between the two is that mysql_query() expects the query to be specified as a null-terminated string whereas mysql_real_query() expects a counted string. If the string contains binary data (which may include null bytes), you must use mysql_real_query().

For each non-SELECT query (for example, INSERT, UPDATE, DELETE), you can find out how many rows were changed (affected) by calling mysql_affected_rows().

For SELECT queries, you retrieve the selected rows as a result set. (Note that some statements are SELECT-like in that they return rows. These include SHOW, DESCRIBE, and EXPLAIN. They should be treated the same way as SELECT statements.)

There are two ways for a client to process result sets. One way is to retrieve the entire result set all at once by calling mysql_store_result(). This function acquires from the server all the rows returned by the query and stores them in the client. The second way is for the client to initiate a row-by-row result set retrieval by calling mysql_use_result(). This function initializes the retrieval, but does not actually get any rows from the server.

In both cases, you access rows by calling mysql_fetch_row(). With mysql_store_result(), mysql_fetch_row() accesses rows that have previously been fetched from the server. With mysql_use_result(), mysql_fetch_row() actually retrieves the row from the server. Information about the size of the data in each row is available by calling mysql_fetch_lengths().

After you are done with a result set, call mysql_free_result() to free the memory used for it.

The two retrieval mechanisms are complementary. Client programs should choose the approach that is most appropriate for their requirements. In practice, clients tend to use mysql_store_result() more commonly.

An advantage of mysql_store_result() is that because the rows have all been fetched to the client, you not only can access rows sequentially, you can move back and forth in the result set using mysql_data_seek() or mysql_row_seek() to change the current row position within the result set. You can also find out how many rows there are by calling mysql_num_rows(). On the other hand, the memory requirements for mysql_store_result() may be very high for large result sets and you are more likely to encounter out-of-memory conditions.

An advantage of mysql_use_result() is that the client requires less memory for the result set because it maintains only one row at a time (and because there is less allocation overhead, mysql_use_result() can be faster). Disadvantages are that you must process each row quickly to avoid tying up the server, you don't have random access to rows within the result set (you can only access rows sequentially), and you don't know how many rows are in the result set until you have retrieved them all. Furthermore, you must retrieve all the rows even if you determine in mid-retrieval that you've found the information you were looking for.

The API makes it possible for clients to respond appropriately to statements (retrieving rows only as necessary) without knowing whether the statement is a SELECT. You can do this by calling mysql_store_result() after each mysql_query() (or mysql_real_query()). If the result set call succeeds, the statement was a SELECT and you can read the rows. If the result set call fails, call mysql_field_count() to determine whether a result was actually to be expected. If mysql_field_count() returns zero, the statement returned no data (indicating that it was an INSERT, UPDATE, DELETE, and so forth), and was not expected to return rows. If mysql_field_count() is non-zero, the statement should have returned rows, but didn't. This indicates that the statement was a SELECT that failed. See the description for mysql_field_count() for an example of how this can be done.

Both mysql_store_result() and mysql_use_result() allow you to obtain information about the fields that make up the result set (the number of fields, their names and types, and so forth). You can access field information sequentially within the row by calling mysql_fetch_field() repeatedly, or by field number within the row by calling mysql_fetch_field_direct(). The current field cursor position may be changed by calling mysql_field_seek(). Setting the field cursor affects subsequent calls to mysql_fetch_field(). You can also get information for fields all at once by calling mysql_fetch_fields().

For detecting and reporting errors, MySQL provides access to error information by means of the mysql_errno() and mysql_error() functions. These return the error code or error message for the most recently invoked function that can succeed or fail, allowing you to determine when an error occurred and what it was.

17.2.3. C API Function Descriptions

17.2.3.1. mysql_affected_rows()
17.2.3.2. mysql_autocommit()
17.2.3.3. mysql_change_user()
17.2.3.4. mysql_character_set_name()
17.2.3.5. mysql_close()
17.2.3.6. mysql_commit()
17.2.3.7. mysql_connect()
17.2.3.8. mysql_create_db()
17.2.3.9. mysql_data_seek()
17.2.3.10. mysql_debug()
17.2.3.11. mysql_drop_db()
17.2.3.12. mysql_dump_debug_info()
17.2.3.13. mysql_eof()
17.2.3.14. mysql_errno()
17.2.3.15. mysql_error()
17.2.3.16. mysql_escape_string()
17.2.3.17. mysql_fetch_field()
17.2.3.18. mysql_fetch_field_direct()
17.2.3.19. mysql_fetch_fields()
17.2.3.20. mysql_fetch_lengths()
17.2.3.21. mysql_fetch_row()
17.2.3.22. mysql_field_count()
17.2.3.23. mysql_field_seek()
17.2.3.24. mysql_field_tell()
17.2.3.25. mysql_free_result()
17.2.3.26. mysql_get_client_info()
17.2.3.27. mysql_get_client_version()
17.2.3.28. mysql_get_host_info()
17.2.3.29. mysql_get_proto_info()
17.2.3.30. mysql_get_server_info()
17.2.3.31. mysql_get_server_version()
17.2.3.32. mysql_hex_string()
17.2.3.33. mysql_info()
17.2.3.34. mysql_init()
17.2.3.35. mysql_insert_id()
17.2.3.36. mysql_kill()
17.2.3.37. mysql_library_end()
17.2.3.38. mysql_library_init()
17.2.3.39. mysql_list_dbs()
17.2.3.40. mysql_list_fields()
17.2.3.41. mysql_list_processes()
17.2.3.42. mysql_list_tables()
17.2.3.43. mysql_more_results()
17.2.3.44. mysql_next_result()
17.2.3.45. mysql_num_fields()
17.2.3.46. mysql_num_rows()
17.2.3.47. mysql_options()
17.2.3.48. mysql_ping()
17.2.3.49. mysql_query()
17.2.3.50. mysql_real_connect()
17.2.3.51. mysql_real_escape_string()
17.2.3.52. mysql_real_query()
17.2.3.53. mysql_refresh()
17.2.3.54. mysql_reload()
17.2.3.55. mysql_rollback()
17.2.3.56. mysql_row_seek()
17.2.3.57. mysql_row_tell()
17.2.3.58. mysql_select_db()
17.2.3.59. mysql_set_character_set()
17.2.3.60. mysql_set_local_infile_default()
17.2.3.61. mysql_set_local_infile_handler()
17.2.3.62. mysql_set_server_option()
17.2.3.63. mysql_shutdown()
17.2.3.64. mysql_sqlstate()
17.2.3.65. mysql_ssl_set()
17.2.3.66. mysql_stat()
17.2.3.67. mysql_store_result()
17.2.3.68. mysql_thread_id()
17.2.3.69. mysql_use_result()
17.2.3.70. mysql_warning_count()

In the descriptions here, a parameter or return value of NULL means NULL in the sense of the C programming language, not a MySQL NULL value.

Functions that return a value generally return a pointer or an integer. Unless specified otherwise, functions returning a pointer return a non-NULL value to indicate success or a NULL value to indicate an error, and functions returning an integer return zero to indicate success or non-zero to indicate an error. Note that “non-zero” means just that. Unless the function description says otherwise, do not test against a value other than zero:

if (result)                   /* correct */
    ... error ...

if (result < 0)               /* incorrect */
    ... error ...

if (result == -1)             /* incorrect */
    ... error ...

When a function returns an error, the Errors subsection of the function description lists the possible types of errors. You can find out which of these occurred by calling mysql_errno(). A string representation of the error may be obtained by calling mysql_error().

MySQL Enterprise MySQL Enterprise subscribers will find more information about the C API functions in the Knowledge Base articles, The C API. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

my_ulonglong mysql_affected_rows(MYSQL *mysql)

Description

After executing a statement with mysql_query() or mysql_real_query(), returns the number of rows changed (for UPDATE), deleted (for DELETE), or inserted (for INSERT). For SELECT statements, mysql_affected_rows() works like mysql_num_rows().

Return Values

An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records were updated for an UPDATE statement, no rows matched the WHERE clause in the query or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_affected_rows() was called prior to calling mysql_store_result(). Because mysql_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

Errors

None.

Example

char *stmt = "UPDATE products SET cost=cost*1.25 WHERE group=10";
mysql_query(&mysql,stmt);
printf("%ld products updated",
       (long) mysql_affected_rows(&mysql));

For UPDATE statements, if you specify the CLIENT_FOUND_ROWS flag when connecting to mysqld, mysql_affected_rows() returns the number of rows matched by the WHERE clause. Otherwise, the default behavior is to return the number of rows actually changed.

Note that when you use a REPLACE command, mysql_affected_rows() returns 2 if the new row replaced an old row, because in this case, one row was inserted after the duplicate was deleted.

If you use INSERT ... ON DUPLICATE KEY UPDATE to insert a row, mysql_affected_rows() returns 1 if the row is inserted as a new row and 2 if an existing row is updated.

my_bool mysql_autocommit(MYSQL *mysql, my_bool mode)

Description

Sets autocommit mode on if mode is 1, off if mode is 0.

This function was added in MySQL 4.1.0.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

my_bool mysql_change_user(MYSQL *mysql, const char *user, const char *password, const char *db)

Description

Changes the user and causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.

This function was introduced in MySQL 3.23.3.

mysql_change_user() fails if the connected user cannot be authenticated or doesn't have permission to use the database. In this case, the user and database are not changed.

The db parameter may be set to NULL if you don't want to have a default database.

Starting from MySQL 4.0.6, this command resets the state as if one had done a new connect. (See Section 17.2.13, “Controlling Automatic Reconnect Behavior”.) It always performs a ROLLBACK of any active transactions, closes and drops all temporary tables, and unlocks all locked tables. Session system variables are reset to the values of the corresponding global system variables. Prepared statements are released and HANDLER variables are closed. Locks acquired with GET_LOCK() are released. These effects occur even if the user didn't change.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

The same that you can get from mysql_real_connect().

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

  • ER_UNKNOWN_COM_ERROR

    The MySQL server doesn't implement this command (probably an old server).

  • ER_ACCESS_DENIED_ERROR

    The user or password was wrong.

  • ER_BAD_DB_ERROR

    The database didn't exist.

  • ER_DBACCESS_DENIED_ERROR

    The user did not have access rights to the database.

  • ER_WRONG_DB_NAME

    The database name was too long.

Example

if (mysql_change_user(&mysql, "user", "password", "new_database"))
{
   fprintf(stderr, "Failed to change user.  Error: %s\n",
           mysql_error(&mysql));
}

const char *mysql_character_set_name(MYSQL *mysql)

Description

Returns the default character set name for the current connection.

Return Values

The default character set name

Errors

None.

17.2.3.5. mysql_close()

void mysql_close(MYSQL *mysql)

Description

Closes a previously opened connection. mysql_close() also deallocates the connection handle pointed to by mysql if the handle was allocated automatically by mysql_init() or mysql_connect().

Return Values

None.

Errors

None.

17.2.3.6. mysql_commit()

my_bool mysql_commit(MYSQL *mysql)

Description

Commits the current transaction.

This function was added in MySQL 4.1.0.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

17.2.3.7. mysql_connect()

MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd)

Description

This function is deprecated. Use mysql_real_connect() instead.

mysql_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_connect() must complete successfully before you can execute any of the other API functions, with the exception of mysql_get_client_info().

The meanings of the parameters are the same as for the corresponding parameters for mysql_real_connect() with the difference that the connection parameter may be NULL. In this case, the C API allocates memory for the connection structure automatically and frees it when you call mysql_close(). The disadvantage of this approach is that you can't retrieve an error message if the connection fails. (To get error information from mysql_errno() or mysql_error(), you must provide a valid MYSQL pointer.)

Return Values

Same as for mysql_real_connect().

Errors

Same as for mysql_real_connect().

int mysql_create_db(MYSQL *mysql, const char *db)

Description

Creates the database named by the db parameter.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL CREATE DATABASE statement instead.

Return Values

Zero if the database was created successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

if(mysql_create_db(&mysql, "my_database"))
{
   fprintf(stderr, "Failed to create new database.  Error: %s\n",
           mysql_error(&mysql));
}

void mysql_data_seek(MYSQL_RES *result, my_ulonglong offset)

Description

Seeks to an arbitrary row in a query result set. The offset value is a row number and should be in the range from 0 to mysql_num_rows(result)-1.

This function requires that the result set structure contains the entire result of the query, so mysql_data_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

None.

Errors

None.

17.2.3.10. mysql_debug()

void mysql_debug(const char *debug)

Description

Does a DBUG_PUSH with the given string. mysql_debug() uses the Fred Fish debug library. To use this function, you must compile the client library to support debugging. See MySQL Internals: Porting.

Return Values

None.

Errors

None.

Example

The call shown here causes the client library to generate a trace file in /tmp/client.trace on the client machine:

mysql_debug("d:t:O,/tmp/client.trace");

17.2.3.11. mysql_drop_db()

int mysql_drop_db(MYSQL *mysql, const char *db)

Description

Drops the database named by the db parameter.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL DROP DATABASE statement instead.

Return Values

Zero if the database was dropped successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

if(mysql_drop_db(&mysql, "my_database"))
  fprintf(stderr, "Failed to drop the database: Error: %s\n",
          mysql_error(&mysql));

int mysql_dump_debug_info(MYSQL *mysql)

Description

Instructs the server to write some debug information to the log. For this to work, the connected user must have the SUPER privilege.

Return Values

Zero if the command was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.13. mysql_eof()

my_bool mysql_eof(MYSQL_RES *result)

Description

This function is deprecated. mysql_errno() or mysql_error() may be used instead.

mysql_eof() determines whether the last row of a result set has been read.

If you acquire a result set from a successful call to mysql_store_result(), the client receives the entire set in one operation. In this case, a NULL return from mysql_fetch_row() always means the end of the result set has been reached and it is unnecessary to call mysql_eof(). When used with mysql_store_result(), mysql_eof() always returns true.

On the other hand, if you use mysql_use_result() to initiate a result set retrieval, the rows of the set are obtained from the server one by one as you call mysql_fetch_row() repeatedly. Because an error may occur on the connection during this process, a NULL return value from mysql_fetch_row() does not necessarily mean the end of the result set was reached normally. In this case, you can use mysql_eof() to determine what happened. mysql_eof() returns a non-zero value if the end of the result set was reached and zero if an error occurred.

Historically, mysql_eof() predates the standard MySQL error functions mysql_errno() and mysql_error(). Because those error functions provide the same information, their use is preferred over mysql_eof(), which is deprecated. (In fact, they provide more information, because mysql_eof() returns only a boolean value whereas the error functions indicate a reason for the error when one occurs.)

Return Values

Zero if no error occurred. Non-zero if the end of the result set has been reached.

Errors

None.

Example

The following example shows how you might use mysql_eof():

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(!mysql_eof(result))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

However, you can achieve the same effect with the standard MySQL error functions:

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(mysql_errno(&mysql))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

17.2.3.14. mysql_errno()

unsigned int mysql_errno(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_errno() returns the error code for the most recently invoked API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. Errors also are listed at Appendix A, Errors, Error Codes, and Common Problems.

Note that some functions like mysql_fetch_row() don't set mysql_errno() if they succeed.

A rule of thumb is that all functions that have to ask the server for information reset mysql_errno() if they succeed.

MySQL-specific error numbers returned by mysql_errno() differ from SQLSTATE values returned by mysql_sqlstate(). For example, the mysql client program displays errors using the following format, where 1146 is the mysql_errno() value and '42S02' is the corresponding mysql_sqlstate() value:

shell> SELECT * FROM no_such_table;
ERROR 1146 (42S02): Table 'test.no_such_table' doesn't exist

Return Values

An error code value for the last mysql_xxx() call, if it failed. zero means no error occurred.

Errors

None.

17.2.3.15. mysql_error()

const char *mysql_error(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_error() returns a null-terminated string containing the error message for the most recently invoked API function that failed. If a function didn't fail, the return value of mysql_error() may be the previous error or an empty string to indicate no error.

A rule of thumb is that all functions that have to ask the server for information reset mysql_error() if they succeed.

For functions that reset mysql_error(), the following two tests are equivalent:

if(*mysql_error(&mysql))
{
  // an error occurred
}

if(mysql_error(&mysql)[0])
{
  // an error occurred
}

The language of the client error messages may be changed by recompiling the MySQL client library. Currently, you can choose error messages in several different languages. See Section 9.3, “Setting the Error Message Language”.

Return Values

A null-terminated character string that describes the error. An empty string if no error occurred.

Errors

None.

You should use mysql_real_escape_string() instead!

This function is identical to mysql_real_escape_string() except that mysql_real_escape_string() takes a connection handler as its first argument and escapes the string according to the current character set. mysql_escape_string() does not take a connection argument and does not respect the current character set.

MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)

Description

Returns the definition of one column of a result set as a MYSQL_FIELD structure. Call this function repeatedly to retrieve information about all columns in the result set. mysql_fetch_field() returns NULL when no more fields are left.

mysql_fetch_field() is reset to return information about the first field each time you execute a new SELECT query. The field returned by mysql_fetch_field() is also affected by calls to mysql_field_seek().

If you've called mysql_query() to perform a SELECT on a table but have not called mysql_store_result(), MySQL returns the default blob length (8KB) if you call mysql_fetch_field() to ask for the length of a BLOB field. (The 8KB size is chosen because MySQL doesn't know the maximum length for the BLOB. This should be made configurable sometime.) Once you've retrieved the result set, field->max_length contains the length of the largest value for this column in the specific query.

Return Values

The MYSQL_FIELD structure for the current column. NULL if no columns are left.

Errors

None.

Example

MYSQL_FIELD *field;

while((field = mysql_fetch_field(result)))
{
    printf("field name %s\n", field->name);
}

MYSQL_FIELD *mysql_fetch_field_direct(MYSQL_RES *result, unsigned int fieldnr)

Description

Given a field number fieldnr for a column within a result set, returns that column's field definition as a MYSQL_FIELD structure. You may use this function to retrieve the definition for an arbitrary column. The value of fieldnr should be in the range from 0 to mysql_num_fields(result)-1.

Return Values

The MYSQL_FIELD structure for the specified column.

Errors

None.

Example

unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *field;

num_fields = mysql_num_fields(result);
for(i = 0; i < num_fields; i++)
{
    field = mysql_fetch_field_direct(result, i);
    printf("Field %u is %s\n", i, field->name);
}

MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *result)

Description

Returns an array of all MYSQL_FIELD structures for a result set. Each structure provides the field definition for one column of the result set.

Return Values

An array of MYSQL_FIELD structures for all columns of a result set.

Errors

None.

Example

unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *fields;

num_fields = mysql_num_fields(result);
fields = mysql_fetch_fields(result);
for(i = 0; i < num_fields; i++)
{
   printf("Field %u is %s\n", i, fields[i].name);
}

unsigned long *mysql_fetch_lengths(MYSQL_RES *result)

Description

Returns the lengths of the columns of the current row within a result set. If you plan to copy field values, this length information is also useful for optimization, because you can avoid calling strlen(). In addition, if the result set contains binary data, you must use this function to determine the size of the data, because strlen() returns incorrect results for any field containing null characters.

The length for empty columns and for columns containing NULL values is zero. To see how to distinguish these two cases, see the description for mysql_fetch_row().

Return Values

An array of unsigned long integers representing the size of each column (not including any terminating null characters). NULL if an error occurred.

Errors

mysql_fetch_lengths() is valid only for the current row of the result set. It returns NULL if you call it before calling mysql_fetch_row() or after retrieving all rows in the result.

Example

MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;

row = mysql_fetch_row(result);
if (row)
{
    num_fields = mysql_num_fields(result);
    lengths = mysql_fetch_lengths(result);
    for(i = 0; i < num_fields; i++)
    {
         printf("Column %u is %lu bytes in length.\n", 
                i, lengths[i]);
    }
}

17.2.3.21. mysql_fetch_row()

MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)

Description

Retrieves the next row of a result set. When used after mysql_store_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve. When used after mysql_use_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve or if an error occurred.

The number of values in the row is given by mysql_num_fields(result). If row holds the return value from a call to mysql_fetch_row(), pointers to the values are accessed as row[0] to row[mysql_num_fields(result)-1]. NULL values in the row are indicated by NULL pointers.

The lengths of the field values in the row may be obtained by calling mysql_fetch_lengths(). Empty fields and fields containing NULL both have length 0; you can distinguish these by checking the pointer for the field value. If the pointer is NULL, the field is NULL; otherwise, the field is empty.

Return Values

A MYSQL_ROW structure for the next row. NULL if there are no more rows to retrieve or if an error occurred.

Errors

Note that error is not reset between calls to mysql_fetch_row()

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;

num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
   unsigned long *lengths;
   lengths = mysql_fetch_lengths(result);
   for(i = 0; i < num_fields; i++)
   {
       printf("[%.*s] ", (int) lengths[i], 
              row[i] ? row[i] : "NULL");
   }
   printf("\n");
}

unsigned int mysql_field_count(MYSQL *mysql)

If you are using a version of MySQL earlier than 3.22.24, you should use unsigned int mysql_num_fields(MYSQL *mysql) instead.

Description

Returns the number of columns for the most recent query on the connection.

The normal use of this function is when mysql_store_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See Section 17.2.14.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

Example

MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if(mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
        else // mysql_store_result() should have returned data
        {
            fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
    }
}

An alternative is to replace the mysql_field_count(&mysql) call with mysql_errno(&mysql). In this case, you are checking directly for an error from mysql_store_result() rather than inferring from the value of mysql_field_count() whether the statement was a SELECT.

17.2.3.23. mysql_field_seek()

MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result, MYSQL_FIELD_OFFSET offset)

Description

Sets the field cursor to the given offset. The next call to mysql_fetch_field() retrieves the field definition of the column associated with that offset.

To seek to the beginning of a row, pass an offset value of zero.

Return Values

The previous value of the field cursor.

Errors

None.

17.2.3.24. mysql_field_tell()

MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)

Description

Returns the position of the field cursor used for the last mysql_fetch_field(). This value can be used as an argument to mysql_field_seek().

Return Values

The current offset of the field cursor.

Errors

None.

void mysql_free_result(MYSQL_RES *result)

Description

Frees the memory allocated for a result set by mysql_store_result(), mysql_use_result(), mysql_list_dbs(), and so forth. When you are done with a result set, you must free the memory it uses by calling mysql_free_result().

Do not attempt to access a result set after freeing it.

Return Values

None.

Errors

None.

const char *mysql_get_client_info(void)

Description

Returns a string that represents the client library version.

Return Values

A character string that represents the MySQL client library version.

Errors

None.

unsigned long mysql_get_client_version(void)

Description

Returns an integer that represents the client library version. The value has the format XYYZZ where X is the major version, YY is the release level, and ZZ is the version number within the release level. For example, a value of 40102 represents a client library version of 4.1.2.

This function was added in MySQL 4.0.16.

Return Values

An integer that represents the MySQL client library version.

Errors

None.

const char *mysql_get_host_info(MYSQL *mysql)

Description

Returns a string describing the type of connection in use, including the server hostname.

Return Values

A character string representing the server hostname and the connection type.

Errors

None.

unsigned int mysql_get_proto_info(MYSQL *mysql)

Description

Returns the protocol version used by current connection.

Return Values

An unsigned integer representing the protocol version used by the current connection.

Errors

None.

const char *mysql_get_server_info(MYSQL *mysql)

Description

Returns a string that represents the server version number.

Return Values

A character string that represents the server version number.

Errors

None.

unsigned long mysql_get_server_version(MYSQL *mysql)

Description

Returns the version number of the server as an integer.

This function was added in MySQL 4.1.0.

Return Values

A number that represents the MySQL server version in this format:

major_version*10000 + minor_version *100 + sub_version

For example, 4.1.2 is returned as 40102.

This function is useful in client programs for quickly determining whether some version-specific server capability exists.

Errors

None.

17.2.3.32. mysql_hex_string()

unsigned long mysql_hex_string(char *to, const char *from, unsigned long length)

Description

This function is used to create a legal SQL string that you can use in an SQL statement. See Section 8.1.1, “Strings”.

The string in from is encoded to hexadecimal format, with each character encoded as two hexadecimal digits. The result is placed in to and a terminating null byte is appended.

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. When mysql_hex_string() returns, the contents of to is a null-terminated string. The return value is the length of the encoded string, not including the terminating null character.

The return value can be placed into an SQL statement using either 0xvalue or X'value' format. However, the return value does not include the 0x or X'...'. The caller must supply whichever of those is desired.

mysql_hex_string() was added in MySQL 4.0.23 and 4.1.8.

Example

char query[1000],*end;

end = strmov(query,"INSERT INTO test_table values(");
end = strmov(end,"0x");
end += mysql_hex_string(end,"What's this",11);
end = strmov(end,",0x");
end += mysql_hex_string(end,"binary data: \0\r\n",16);
*end++ = ')';

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The strmov() function used in the example is included in the mysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the value placed into to, not including the terminating null character.

Errors

None.

17.2.3.33. mysql_info()

const char *mysql_info(MYSQL *mysql)

Description

Retrieves a string providing information about the most recently executed statement, but only for the statements listed here. For other statements, mysql_info() returns NULL. The format of the string varies depending on the type of statement, as described here. The numbers are illustrative only; the string contains values appropriate for the statement.

  • INSERT INTO ... SELECT ...

    String format: Records: 100 Duplicates: 0 Warnings: 0

  • INSERT INTO ... VALUES (...),(...),(...)...

    String format: Records: 3 Duplicates: 0 Warnings: 0

  • LOAD DATA INFILE ...

    String format: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0

  • ALTER TABLE

    String format: Records: 3 Duplicates: 0 Warnings: 0

  • UPDATE

    String format: Rows matched: 40 Changed: 40 Warnings: 0

Note that mysql_info() returns a non-NULL value for INSERT ... VALUES only for the multiple-row form of the statement (that is, only if multiple value lists are specified).

Return Values

A character string representing additional information about the most recently executed statement. NULL if no information is available for the statement.

Errors

None.

17.2.3.34. mysql_init()

MYSQL *mysql_init(MYSQL *mysql)

Description

Allocates or initializes a MYSQL object suitable for mysql_real_connect(). If mysql is a NULL pointer, the function allocates, initializes, and returns a new object. Otherwise, the object is initialized and the address of the object is returned. If mysql_init() allocates a new object, it is freed when mysql_close() is called to close the connection.

Return Values

An initialized MYSQL* handle. NULL if there was insufficient memory to allocate a new object.

Errors

In case of insufficient memory, NULL is returned.

17.2.3.35. mysql_insert_id()

my_ulonglong mysql_insert_id(MYSQL *mysql)

Description

Returns the value generated for an AUTO_INCREMENT column by the previous INSERT or UPDATE statement. Use this function after you have performed an INSERT statement into a table that contains an AUTO_INCREMENT field, or have used INSERT or UPDATE to set a column value with LAST_INSERT_ID(expr).

More precisely, mysql_insert_id() is updated under these conditions:

  • INSERT statements that store a value into an AUTO_INCREMENT column. This is true whether the value is automatically generated by storing the special values NULL or 0 into the column, or is an explicit non-special value.

  • In the case of a multiple-row INSERT statement, mysql_insert_id() returns the first automatically generated AUTO_INCREMENT value; if no such value is generated, it returns the last explicit value inserted into the AUTO_INCREMENT column.

  • INSERT statements that generate an AUTO_INCREMENT value by inserting LAST_INSERT_ID(expr) into any column or by updating any column to LAST_INSERT_ID(expr).

  • If the previous statement returned an error, the value of mysql_insert_id() is undefined.

mysql_insert_id() returns 0 if the previous statement does not use an AUTO_INCREMENT value. If you need to save the value for later, be sure to call mysql_insert_id() immediately after the statement that generates the value.

The value of mysql_insert_id() is not affected by statements such as SELECT that return a result set.

The value of mysql_insert_id() is affected only by statements issued within the current client connection. It is not affected by statements issued by other clients.

The LAST_INSERT_ID() SQL function returns the most recently generated AUTO_INCREMENT value, and is not reset between statements because the value of that function is maintained in the server. Another difference from mysql_insert_id() is that LAST_INSERT_ID() is not updated if you set an AUTO_INCREMENT column to a specific non-special value. See Section 11.10.3, “Information Functions”.

The reason for the differences between LAST_INSERT_ID() and mysql_insert_id() is that LAST_INSERT_ID() is made easy to use in scripts while mysql_insert_id() tries to provide more exact information about what happens to the AUTO_INCREMENT column.

Return Values

Described in the preceding discussion.

Errors

None.

17.2.3.36. mysql_kill()

int mysql_kill(MYSQL *mysql, unsigned long pid)

Description

Asks the server to kill the thread specified by pid.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL KILL statement instead.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

void mysql_library_end(void)

Description

This function finalizes the MySQL library. You should call it when you are done using the library (for example, after disconnecting from the server). The action taken by the call depends on whether your application is linked to the MySQL client library or the MySQL embedded server library. For a client program linked against the libmysqlclient library by using the -lmysqlclient flag, mysql_library_end() performs some memory management to clean up. For an embedded server application linked against the libmysqld library by using the -lmysqld flag, mysql_library_end() shuts down the embedded server and then cleans up.

See Section 17.2.2, “C API Function Overview”, and Section 17.2.3.38, “mysql_library_init(), for usage information.

mysql_library_end() was added in MySQL 4.1.10. For older versions of MySQL, call mysql_server_end() instead.

int mysql_library_init(int argc, char **argv, char **groups)

Description

This function should be called to initialize the MySQL library before you call any other MySQL function. If your application uses the embedded server, this call starts the server and initializes any subsystems (mysys, InnoDB, and so forth) that the server uses.

In a non-multi-threaded environment, the call to mysql_library_init() may be omitted, because mysql_init() will invoke it automatically as necessary. However, mysql_library_init() is not thread-safe in a multi-threaded environment, and thus neither is mysql_init(), which calls mysql_library_init(). You must either call mysql_library_init() prior to spawning any threads, or else use a mutex to protect the call, whether you invoke mysql_library_init() or indirectly via mysql_init(). This should be done prior to any other client library call.

After your application is done using the MySQL library, call mysql_library_end() to clean up. See Section 17.2.3.37, “mysql_library_end().

The argc and argv arguments are analogous to the arguments to main(). The first element of argv is ignored (it typically contains the program name). For convenience, argc may be 0 (zero) if there are no command-line arguments for the server. mysql_library_init() makes a copy of the arguments so it is safe to destroy argv or groups after the call.

If you want to connect to an external server without starting the embedded server, you have to specify a negative value for argc.

The groups argument should be an array of strings that indicate the groups in option files from which options should be read. See Section 4.2.3.2, “Using Option Files”. The final entry in the array should be NULL. For convenience, if the groups argument itself is NULL, the [server] and [embedded] groups are used by default.

See Section 17.2.2, “C API Function Overview”, for additional usage information.

mysql_library_init() was added in MySQL 4.1.10. For older versions of MySQL, call mysql_server_init() instead.

Example

#include <mysql.h>
#include <stdlib.h>

static char *server_args[] = {
  "this_program",       /* this string is not used */
  "--datadir=.",
  "--key_buffer_size=32M"
};
static char *server_groups[] = {
  "embedded",
  "server",
  "this_program_SERVER",
  (char *)NULL
};

int main(void) {
  if (mysql_library_init(sizeof(server_args) / sizeof(char *),
                        server_args, server_groups)) {
    fprintf(stderr, "could not initialize MySQL library\n");
    exit(1);
  }

  /* Use any MySQL API functions here */

  mysql_library_end();

  return EXIT_SUCCESS;
}

Return Values

Zero if successful. Non-zero if an error occurred.

17.2.3.39. mysql_list_dbs()

MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of database names on the server that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters “%” or “_”, or may be a NULL pointer to match all databases. Calling mysql_list_dbs() is similar to executing the query SHOW databases [LIKE wild].

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild)

Description

Returns a result set consisting of field names in the given table that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters “%” or “_”, or may be a NULL pointer to match all fields. Calling mysql_list_fields() is similar to executing the query SHOW COLUMNS FROM tbl_name [LIKE wild].

Note that it's recommended that you use SHOW COLUMNS FROM tbl_name instead of mysql_list_fields().

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

MYSQL_RES *mysql_list_processes(MYSQL *mysql)

Description

Returns a result set describing the current server threads. This is the same kind of information as that reported by mysqladmin processlist or a SHOW PROCESSLIST query.

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of table names in the current database that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters “%” or “_”, or may be a NULL pointer to match all tables. Calling mysql_list_tables() is similar to executing the query SHOW tables [LIKE wild].

You must free the result set with mysql_free_result().

mysql_num_rows() is intended for use with statements that return a result set, such as SELECT. For statements such as INSERT, UPDATE, or DELETE, the number of affected rows can be obtained with mysql_affected_rows().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

my_bool mysql_more_results(MYSQL *mysql)

Description

This function is used when you execute multiple statements specified as a single statement string.

mysql_more_results() true if more results exist from the currently executed statement, in which case the application must call mysql_next_result() to fetch the results.

This function was added in MySQL 4.1.0.

Return Values

TRUE (1) if more results exist. FALSE (0) if no more results exist.

In most cases, you can call mysql_next_result() instead to test whether more results exist and initiate retrieval if so.

See Section 17.2.9, “C API Handling of Multiple Statement Execution”, and Section 17.2.3.44, “mysql_next_result().

Errors

None.

int mysql_next_result(MYSQL *mysql)

Description

This function is used when you execute multiple statements specified as a single statement string.

If more statement results exist, mysql_next_result() reads the next statement result and returns the status back to the application.

Before calling mysql_next_result(), you must call mysql_free_result() for the preceding statement if it is a query that returned a result set.

After calling mysql_next_result() the state of the connection is as if you had called mysql_real_query() or mysql_query() for the next statement. This means that you can call mysql_store_result(), mysql_warning_count(), mysql_affected_rows(), and so forth.

If mysql_next_result() returns an error, no other statements are executed and there are no more results to fetch.

For an example that shows how to use mysql_next_result(), see Section 17.2.9, “C API Handling of Multiple Statement Execution”.

This function was added in MySQL 4.1.0.

Return Values

Return ValueDescription
0Successful and there are more results
-1Successful and there are no more results
>0An error occurred

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order. For example if you didn't call mysql_use_result() for a previous result set.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.45. mysql_num_fields()

unsigned int mysql_num_fields(MYSQL_RES *result)

Or:

unsigned int mysql_num_fields(MYSQL *mysql)

The second form doesn't work on MySQL 3.22.24 or newer. To pass a MYSQL* argument, you must use unsigned int mysql_field_count(MYSQL *mysql) instead.

Description

Returns the number of columns in a result set.

Note that you can get the number of columns either from a pointer to a result set or to a connection handle. You would use the connection handle if mysql_store_result() or mysql_use_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See Section 17.2.14.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

Example

MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if (mysql_errno(&mysql))
        {
           fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
        else if (mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
    }
}

An alternative (if you know that your query should have returned a result set) is to replace the mysql_errno(&mysql) call with a check whether mysql_field_count(&mysql) returns 0. This happens only if something went wrong.

17.2.3.46. mysql_num_rows()

my_ulonglong mysql_num_rows(MYSQL_RES *result)

Description

Returns the number of rows in the result set.

The use of mysql_num_rows() depends on whether you use mysql_store_result() or mysql_use_result() to return the result set. If you use mysql_store_result(), mysql_num_rows() may be called immediately. If you use mysql_use_result(), mysql_num_rows() does not return the correct value until all the rows in the result set have been retrieved.

Return Values

The number of rows in the result set.

Errors

None.

17.2.3.47. mysql_options()

int mysql_options(MYSQL *mysql, enum mysql_option option, const char *arg)

Description

Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options.

mysql_options() should be called after mysql_init() and before mysql_connect() or mysql_real_connect().

The option argument is the option that you want to set; the arg argument is the value for the option. If the option is an integer, arg should point to the value of the integer.

The following list describes the possible options, their effect, and how arg is used for each option. Several of the options apply only when the application is linked against the libmysqld embedded server library and are unused for applications linked against the libmysql client library. For option descriptions that indicate arg is unused, its value is irrelevant; it is conventional to pass 0.

  • MYSQL_INIT_COMMAND (argument type: char *)

    Statement to execute when connecting to the MySQL server. Automatically re-executed if reconnection occurs.

  • MYSQL_OPT_COMPRESS (argument: not used)

    Use the compressed client/server protocol.

  • MYSQL_OPT_CONNECT_TIMEOUT (argument type: unsigned int *)

    Connect timeout in seconds.

  • MYSQL_OPT_GUESS_CONNECTION (argument: not used)

    For an application linked against the libmysqld embedded server library, this allows the library to “guess” whether to use the embedded server or a remote server. “Guess” means that if the hostname is set and is not localhost, it uses a remote server. This behavior is the default. MYSQL_OPT_USE_EMBEDDED_CONNECTION and MYSQL_OPT_USE_REMOTE_CONNECTION can be used to override it. This option is ignored for applications linked against the libmysqlclient client library. Available starting in 4.1.1.

  • MYSQL_OPT_LOCAL_INFILE (argument type: optional pointer to unsigned int)

    If no pointer is given or if pointer points to an unsigned int that has a non-zero value, the LOAD LOCAL INFILE statement is enabled.

  • MYSQL_OPT_NAMED_PIPE (argument: not used)

    Use named pipes to connect to a MySQL server on Windows, if the server allows named-pipe connections.

  • MYSQL_OPT_PROTOCOL (argument type: unsigned int *)

    Type of protocol to use. Should be one of the enum values of mysql_protocol_type defined in mysql.h. Added in 4.1.0.

  • MYSQL_OPT_READ_TIMEOUT (argument type: unsigned int *)

    The timeout in seconds for attempts to read from the server. Each attempt uses this timeout value and there are retries if necessary, so the total effective timeout value is three times the option value. You can set the value so that a lost connection can be detected earlier than the TCP/IP Close_Wait_Timeout value of 10 minutes. This option works only for TCP/IP connections, and only for Windows prior to MySQL 4.1.22. Added in 4.1.1.

  • MYSQL_OPT_SET_CLIENT_IP (argument type: char *)

    For an application linked against the libmysqld embedded server library (when libmysqld is compiled with authentication support), this means that the user is considered to have connected from the specified IP address (specified as a string) for authentication purposes. This option is ignored for applications linked against the libmysqlclient client library. Added in 4.1.1.

  • MYSQL_OPT_USE_EMBEDDED_CONNECTION (argument: not used)

    For an application linked against the libmysqld embedded server library, this forces the use of the embedded server for the connection. This option is ignored for applications linked against the libmysqlclient client library. Added in 4.1.1.

  • MYSQL_OPT_USE_REMOTE_CONNECTION (argument: not used)

    For an application linked against the libmysqld embedded server library, this forces the use of a remote server for the connection. This option is ignored for applications linked against the libmysqlclient client library. Added in 4.1.1.

  • MYSQL_OPT_USE_RESULT (argument: not used)

    This option is available beginning with MySQL 4.1.1, but is unused.

  • MYSQL_OPT_WRITE_TIMEOUT (argument type: unsigned int *)

    The timeout in seconds for attempts to write to the server. Each attempt uses this timeout value and there are net_retry_count retries if necessary, so the total effective timeout value is net_retry_count times the option value. This option works only on Windows for TCP/IP connections. Added in 4.1.1.

  • MYSQL_READ_DEFAULT_FILE (argument type: char *)

    Read options from the named option file instead of from my.cnf.

  • MYSQL_READ_DEFAULT_GROUP (argument type: char *)

    Read options from the named group from my.cnf or the file specified with MYSQL_READ_DEFAULT_FILE.

  • MYSQL_REPORT_DATA_TRUNCATION (argument type: my_bool *)

    Enable or disable reporting of data truncation errors for prepared statements via MYSQL_BIND.error. (Default: disabled.)

  • MYSQL_SECURE_AUTH (argument type: my_bool*)

    Whether to connect to a server that does not support the improved password hashing available beginning in MySQL 4.1.1. This option was added in MySQL 4.1.1.

  • MYSQL_SET_CHARSET_DIR (argument type: char *)

    The pathname to the directory that contains character set definition files.

  • MYSQL_SET_CHARSET_NAME (argument type: char *)

    The name of the character set to use as the default character set.

  • MYSQL_SHARED_MEMORY_BASE_NAME (argument type: char *)

    The name of the shared-memory object for communication to the server on Windows, if the server supports shared-memory connections. Should have the same value as the --shared-memory-base-name option used for the mysqld server you want to connect to. Added in 4.1.0.

The client group is always read if you use MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.

The specified group in the option file may contain the following options:

OptionDescription
character-sets-dir=pathThe directory where character sets are installed.
compressUse the compressed client/server protocol.
connect-timeout=secondsConnect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server.
database=db_nameConnect to this database if no database was specified in the connect command.
debugDebug options.
default-character-set=charset_nameThe default character set to use.
disable-local-infileDisable use of LOAD DATA LOCAL.
host=host_nameDefault hostname.
init-command=stmtStatement to execute when connecting to MySQL server. Automatically re-executed if reconnection occurs.
interactive-timeout=secondsSame as specifying CLIENT_INTERACTIVE to mysql_real_connect(). See Section 17.2.3.50, “mysql_real_connect().
local-infile[={0|1}]If no argument or non-zero argument, enable use of LOAD DATA LOCAL; otherwise disable.
max_allowed_packet=bytesMaximum size of packet that client can read from server.
multi-resultsAllow multiple result sets from multiple-statement executions or stored procedures. Added in 4.1.1.
multi-queries, multi-resultsAllow the client to send multiple statements in a single string (separated by “;”). Added in 4.1.9.
password=passwordDefault password.
pipeUse named pipes to connect to a MySQL server on NT.
port=port_numDefault port number.
protocol={TCP|SOCKET|PIPE|MEMORY}The protocol to use when connecting to the server. (Added in MySQL 4.1)
return-found-rowsTell mysql_info() to return found rows instead of updated rows when using UPDATE.
shared-memory-base-name=nameShared-memory name to use to connect to server. Added in MySQL 4.1.
socket=pathDefault socket file.
ssl-ca=file_nameCertificate Authority file.
ssl-capath=pathCertificate Authority directory.
ssl-cert=file_nameCertificate file.
ssl-cipher=cipher_listAllowable SSL ciphers.
ssl-key=file_nameKey file.
timeout=secondsLike connect-timeout.
userDefault user.

timeout has been replaced by connect-timeout, but timeout is still supported in MySQL 4.1 for backward compatibility.

For more information about option files, see Section 4.2.3.2, “Using Option Files”.

Return Values

Zero for success. Non-zero if you specify an unknown option.

Example

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_COMPRESS,0);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

This code requests that the client use the compressed client/server protocol and read the additional options from the odbc section in the my.cnf file.

17.2.3.48. mysql_ping()

int mysql_ping(MYSQL *mysql)

Description

Checks whether the connection to the server is working. If the connection has gone down, an attempt to reconnect is made unless auto-reconnect is disabled.

This function can be used by clients that remain idle for a long while, to check whether the server has closed the connection and reconnect if necessary.

Return Values

Zero if the connection to the server is alive. Non-zero if an error occurred. A non-zero return does not indicate whether the MySQL server itself is down; the connection might be broken for other reasons such as network problems.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.49. mysql_query()

int mysql_query(MYSQL *mysql, const char *stmt_str)

Description

Executes the SQL statement pointed to by the null-terminated string stmt_str. Normally, the string must consist of a single SQL statement and you should not add a terminating semicolon (“;”) or \g to the statement. If multiple-statement execution has been enabled, the string can contain several statements separated by semicolons. See Section 17.2.9, “C API Handling of Multiple Statement Execution”.

mysql_query() cannot be used for statements that contain binary data; you must use mysql_real_query() instead. (Binary data may contain the “\0” character, which mysql_query() interprets as the end of the statement string.)

If you want to know whether the statement should return a result set, you can use mysql_field_count() to check for this. See Section 17.2.3.22, “mysql_field_count().

Return Values

Zero if the statement was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned long client_flag)

Description

mysql_real_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_real_connect() must complete successfully before you can execute any other API functions that require a valid MYSQL connection handle structure.

The parameters are specified as follows:

  • The first parameter should be the address of an existing MYSQL structure. Before calling mysql_real_connect() you must call mysql_init() to initialize the MYSQL structure. You can change a lot of connect options with the mysql_options() call. See Section 17.2.3.47, “mysql_options().

  • The value of host may be either a hostname or an IP address. If host is NULL or the string "localhost", a connection to the local host is assumed. For Windows, the client connects using a shared-memory connection, if the server has shared-memory connections enabled. Otherwise, TCP/IP is used. For Unix, the client connects using a Unix socket file. For local connections, you can also influence the type of connection to use with the MYSQL_OPT_PROTOCOL or MYSQL_OPT_NAMED_PIPE options to mysql_options(). The type of connection must be supported by the server. For a host value of "." on Windows, the client connects using a named pipe, if the server has named-pipe connections enabled. If named-pipe connections are not enabled, an error occurs.

  • The user parameter contains the user's MySQL login ID. If user is NULL or the empty string "", the current user is assumed. Under Unix, this is the current login name. Under Windows ODBC, the current username must be specified explicitly. See the MyODBC section of Chapter 18, Connectors.

  • The passwd parameter contains the password for user. If passwd is NULL, only entries in the user table for the user that have a blank (empty) password field are checked for a match. This allows the database administrator to set up the MySQL privilege system in such a way that users get different privileges depending on whether they have specified a password.

    Note

    Do not attempt to encrypt the password before calling mysql_real_connect(); password encryption is handled automatically by the client API.

  • The user and passwd parameters use whatever character set has been configured for the MYSQL object. By default, this is latin1, but can be changed by calling mysql_options(mysql, MYSQL_SET_CHARSET_NAME, "charset_name") prior to connecting.

  • db is the database name. If db is not NULL, the connection sets the default database to this value.

  • If port is not 0, the value is used as the port number for the TCP/IP connection. Note that the host parameter determines the type of the connection.

  • If unix_socket is not NULL, the string specifies the socket or named pipe that should be used. Note that the host parameter determines the type of the connection.

  • The value of client_flag is usually 0, but can be set to a combination of the following flags to enable certain features:

    Flag NameFlag Description
    CLIENT_COMPRESSUse compression protocol.
    CLIENT_FOUND_ROWSReturn the number of found (matched) rows, not the number of changed rows.
    CLIENT_IGNORE_SIGPIPEPrevents the client library from installing a SIGPIPE signal handler. This can be used to avoid conflicts with a handler that the application has already installed.
    CLIENT_IGNORE_SPACEAllow spaces after function names. Makes all functions names reserved words.
    CLIENT_INTERACTIVEAllow interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection. The client's session wait_timeout variable is set to the value of the session interactive_timeout variable.
    CLIENT_LOCAL_FILESEnable LOAD DATA LOCAL handling.
    CLIENT_MULTI_RESULTSTell the server that the client can handle multiple result sets from multiple-statement executions. This is automatically set if CLIENT_MULTI_STATEMENTS is set. See the note following this table for more information about this flag. Added in MySQL 4.1.
    CLIENT_MULTI_STATEMENTSTell the server that the client may send multiple statements in a single string (separated by “;”). If this flag is not set, multiple-statement execution is disabled. See the note following this table for more information about this flag. Added in MySQL 4.1.
    CLIENT_NO_SCHEMADon't allow the db_name.tbl_name.col_name syntax. This is for ODBC. It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs.
    CLIENT_ODBCUnused.
    CLIENT_SSLUse SSL (encrypted protocol). This option should not be set by application programs; it is set internally in the client library. Instead, use mysql_ssl_set() before calling mysql_real_connect().

If you enable CLIENT_MULTI_STATEMENTS or CLIENT_MULTI_RESULTS, you should process the result for every call to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 17.2.9, “C API Handling of Multiple Statement Execution”.

For some parameters, it is possible to have the value taken from an option file rather than from an explicit value in the mysql_real_connect() call. To do this, call mysql_options() with the MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP option before calling mysql_real_connect(). Then, in the mysql_real_connect() call, specify the “no-value” value for each parameter to be read from an option file:

  • For host, specify a value of NULL or the empty string ("").

  • For user, specify a value of NULL or the empty string.

  • For passwd, specify a value of NULL. (For the password, a value of the empty string in the mysql_real_connect() call cannot be overridden in an option file, because the empty string indicates explicitly that the MySQL account must have an empty password.)

  • For db, specify a value of NULL or the empty string.

  • For port, specify a value of 0.

  • For unix_socket, specify a value of NULL.

If no value is found in an option file for a parameter, its default value is used as indicated in the descriptions given earlier in this section.

Return Values

A MYSQL* connection handle if the connection was successful, NULL if the connection was unsuccessful. For a successful connection, the return value is the same as the value of the first parameter.

Errors

  • CR_CONN_HOST_ERROR

    Failed to connect to the MySQL server.

  • CR_CONNECTION_ERROR

    Failed to connect to the local MySQL server.

  • CR_IPSOCK_ERROR

    Failed to create an IP socket.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SOCKET_CREATE_ERROR

    Failed to create a Unix socket.

  • CR_UNKNOWN_HOST

    Failed to find the IP address for the hostname.

  • CR_VERSION_ERROR

    A protocol mismatch resulted from attempting to connect to a server with a client library that uses a different protocol version. This can happen if you use a very old client library to connect to a new server that wasn't started with the --old-protocol option.

  • CR_NAMEDPIPEOPEN_ERROR

    Failed to create a named pipe on Windows.

  • CR_NAMEDPIPEWAIT_ERROR

    Failed to wait for a named pipe on Windows.

  • CR_NAMEDPIPESETSTATE_ERROR

    Failed to get a pipe handler on Windows.

  • CR_SERVER_LOST

    If connect_timeout > 0 and it took longer than connect_timeout seconds to connect to the server or if the server died while executing the init-command.

Example

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

By using mysql_options() the MySQL library reads the [client] and [your_prog_name] sections in the my.cnf file which ensures that your program works, even if someone has set up MySQL in some non-standard way.

Note that upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1. A value of 1 for this flag indicates that if a statement cannot be performed because of a lost connection, to try reconnecting to the server before giving up.

unsigned long mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned long length)

Note that mysql must be a valid, open connection. This is needed because the escaping depends on the character set in use by the server.

Description

This function is used to create a legal SQL string that you can use in an SQL statement. See Section 8.1.1, “Strings”.

The string in from is encoded to an escaped SQL string, taking into account the current character set of the connection. The result is placed in to and a terminating null byte is appended. Characters encoded are NUL (ASCII 0), “\n”, “\r”, “\”, “'”, “"”, and Control-Z (see Section 8.1, “Literal Values”). (Strictly speaking, MySQL requires only that backslash and the quote character used to quote the string in the query be escaped. This function quotes the other characters to make them easier to read in log files.)

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. (In the worst case, each character may need to be encoded as using two bytes, and you need room for the terminating null byte.) When mysql_real_escape_string() returns, the contents of to is a null-terminated string. The return value is the length of the encoded string, not including the terminating null character.

If you need to change the character set of the connection, you should use the mysql_set_character_set() function rather than executing a SET NAMES (or SET CHARACTER SET) statement. mysql_set_character_set() works like SET NAMES but also affects the character set used by mysql_real_escape_string(), which SET NAMES does not.

Example

char query[1000],*end;

end = strmov(query,"INSERT INTO test_table values(");
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"What's this",11);
*end++ = '\'';
*end++ = ',';
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"binary data: \0\r\n",16);
*end++ = '\'';
*end++ = ')';

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The strmov() function used in the example is included in the mysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the value placed into to, not including the terminating null character.

Errors

None.

17.2.3.52. mysql_real_query()

int mysql_real_query(MYSQL *mysql, const char *stmt_str, unsigned long length)

Description

Executes the SQL statement pointed to by stmt_str, which should be a string length bytes long. Normally, the string must consist of a single SQL statement and you should not add a terminating semicolon (“;”) or \g to the statement. If multiple-statement execution has been enabled, the string can contain several statements separated by semicolons. See Section 17.2.9, “C API Handling of Multiple Statement Execution”.

mysql_query() cannot be used for statements that contain binary data; you must use mysql_real_query() instead. (Binary data may contain the “\0” character, which mysql_query() interprets as the end of the statement string.) In addition, mysql_real_query() is faster than mysql_query() because it does not call strlen() on the statement string.

If you want to know whether the statement should return a result set, you can use mysql_field_count() to check for this. See Section 17.2.3.22, “mysql_field_count().

Return Values

Zero if the statement was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.53. mysql_refresh()

int mysql_refresh(MYSQL *mysql, unsigned int options)

Description

This function flushes tables or caches, or resets replication server information. The connected user must have the RELOAD privilege.

The options argument is a bit mask composed from any combination of the following values. Multiple values can be OR'ed together to perform multiple operations with a single call.

  • REFRESH_GRANT

    Refresh the grant tables, like FLUSH PRIVILEGES.

  • REFRESH_LOG

    Flush the logs, like FLUSH LOGS.

  • REFRESH_TABLES

    Flush the table cache, like FLUSH TABLES.

  • REFRESH_HOSTS

    Flush the host cache, like FLUSH HOSTS.

  • REFRESH_STATUS

    Reset status variables, like FLUSH STATUS.

  • REFRESH_THREADS

    Flush the thread cache.

  • REFRESH_SLAVE

    On a slave replication server, reset the master server information and restart the slave, like RESET SLAVE.

  • REFRESH_MASTER

    On a master replication server, remove the binary log files listed in the binary log index and truncate the index file, like RESET MASTER.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.54. mysql_reload()

int mysql_reload(MYSQL *mysql)

Description

Asks the MySQL server to reload the grant tables. The connected user must have the RELOAD privilege.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL FLUSH PRIVILEGES statement instead.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.55. mysql_rollback()

my_bool mysql_rollback(MYSQL *mysql)

Description

Rolls back the current transaction.

This function was added in MySQL 4.1.0.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

17.2.3.56. mysql_row_seek()

MYSQL_ROW_OFFSET mysql_row_seek(MYSQL_RES *result, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a query result set. The offset value is a row offset that should be a value returned from mysql_row_tell() or from mysql_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_row_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_row_seek().

Errors

None.

17.2.3.57. mysql_row_tell()

MYSQL_ROW_OFFSET mysql_row_tell(MYSQL_RES *result)

Description

Returns the current position of the row cursor for the last mysql_fetch_row(). This value can be used as an argument to mysql_row_seek().

You should use mysql_row_tell() only after mysql_store_result(), not after mysql_use_result().

Return Values

The current offset of the row cursor.

Errors

None.

17.2.3.58. mysql_select_db()

int mysql_select_db(MYSQL *mysql, const char *db)

Description

Causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.

mysql_select_db() fails unless the connected user can be authenticated as having permission to use the database.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

int mysql_set_character_set(MYSQL *mysql, const char *csname)

Description

This function is used to set the default character set for the current connection. The string csname specifies a valid character set name. The connection collation becomes the default collation of the character set. This function works like the SET NAMES statement, but also sets the value of mysql->charset, and thus affects the character set used by mysql_real_escape_string()

This function was added in MySQL 4.1.13.

Return Values

Zero for success. Non-zero if an error occurred.

Example

MYSQL mysql;

mysql_init(&mysql);
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

if (!mysql_set_character_set(&mysql, "utf8")) 
{
    printf("New client character set: %s\n", 
           mysql_character_set_name(&mysql));
}

void mysql_set_local_infile_default(MYSQL *mysql);

Description

Sets the LOAD LOCAL DATA INFILE handler callback functions to the defaults used internally by the C client library. The library calls this function automatically if mysql_set_local_infile_handler() has not been called or does not supply valid functions for each of its callbacks.

The mysql_set_local_infile_default() function was added in MySQL 4.1.2.

Return Values

None.

Errors

None.

void mysql_set_local_infile_handler(MYSQL *mysql, int (*local_infile_init)(void **, const char *, void *), int (*local_infile_read)(void *, char *, unsigned int), void (*local_infile_end)(void *), int (*local_infile_error)(void *, char*, unsigned int), void *userdata);

Description

This function installs callbacks to be used during the execution of LOAD DATA LOCAL INFILE statements. It enables application programs to exert control over local (client-side) data file reading. The arguments are the connection handler, a set of pointers to callback functions, and a pointer to a data area that the callbacks can use to share information.

To use mysql_set_local_infile_handler(), you must write the following callback functions:

int
local_infile_init(void **ptr, const char *filename, void *userdata);

The initialization function. This is called once to do any setup necessary, open the data file, allocate data structures, and so forth. The first void** argument is a pointer to a pointer. You can set the pointer (that is, *ptr) to a value that will be passed to each of the other callbacks (as a void*). The callbacks can use this pointed-to value to maintain state information. The userdata argument is the same value that is passed to mysql_set_local_infile_handler().

The initialization function should return zero for success, non-zero for an error.

int
local_infile_read(void *ptr, char *buf, unsigned int buf_len);

The data-reading function. This is called repeatedly to read the data file. buf points to the buffer where the read data should be stored, and buf_len is the maximum number of bytes that the callback can read and store in the buffer. (It can read fewer bytes, but should not read more.)

The return value is the number of bytes read, or zero when no more data could be read (this indicates EOF). Return a value less than zero if an error occurs.

void
local_infile_end(void *ptr)

The termination function. This is called once after local_infile_read() has returned zero (EOF) or an error. This function should deallocate any memory allocated by local_infile_init() and perform any other cleanup necessary. It is invoked even if the initalization function returns an error.

int
local_infile_error(void *ptr, 
                   char *error_msg, 
                   unsigned int error_msg_len);

The error-handling function. This is called to get a textual error message to return to the user in case any of your other functions returns an error. error_msg points to the buffer into which the message should be written, and error_msg_len is the length of the buffer. The message should be written as a null-terminated string, so the message can be at most error_msg_len–1 bytes long.

The return value is the error number.

Typically, the other callbacks store the error message in the data structure pointed to by ptr, so that local_infile_error() can copy the message from there into error_msg.

After calling mysql_set_local_infile_handler() in your C code and passing pointers to your callback functions, you can then issue a LOAD DATA LOCAL INFILE statement (for example, by using mysql_query()). The client library automatically invokes your callbacks. The filename specified in LOAD DATA LOCAL INFILE will be passed as the second parameter to the local_infile_init() callback.

The mysql_set_local_infile_handler() function was added in MySQL 4.1.2.

Return Values

None.

Errors

None.

int mysql_set_server_option(MYSQL *mysql, enum enum_mysql_set_option option)

Description

Enables or disables an option for the connection. option can have one of the following values:

MYSQL_OPTION_MULTI_STATEMENTS_ONEnable multiple-statement support
MYSQL_OPTION_MULTI_STATEMENTS_OFFDisable multiple-statement support

If you enable multiple-statement support, you should retrieve results from calls to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 17.2.9, “C API Handling of Multiple Statement Execution”.

Enabling multiple-statement support with MYSQL_OPTION_MULTI_STATEMENTS_ON does not have quite the same effect as enabling it by passing the CLIENT_MULTI_STATEMENTS flag to mysql_real_connect(): CLIENT_MULTI_STATEMENTS also enables CLIENT_MULTI_RESULTS.

This function was added in MySQL 4.1.1.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • ER_UNKNOWN_COM_ERROR

    The server didn't support mysql_set_server_option() (which is the case that the server is older than 4.1.1) or the server didn't support the option one tried to set.

17.2.3.63. mysql_shutdown()

int mysql_shutdown(MYSQL *mysql, enum mysql_enum_shutdown_level shutdown_level)

Description

Asks the database server to shut down. The connected user must have SHUTDOWN privileges. The shutdown_level argument was added in MySQL 4.1.3. MySQL 4.1 supports only one type of shutdown; shutdown_level must be equal to SHUTDOWN_DEFAULT. Additional shutdown levels are planned to make it possible to choose the desired level. Dynamically linked executables which have been compiled with older versions of the libmysqlclient headers and call mysql_shutdown() need to be used with the old libmysqlclient dynamic library.

The shutdown process is described in Section 5.1.10, “The Shutdown Process”.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.64. mysql_sqlstate()

const char *mysql_sqlstate(MYSQL *mysql)

Description

Returns a null-terminated string containing the SQLSTATE error code for the most recently executed SQL statement. The error code consists of five characters. '00000' means “no error.” The values are specified by ANSI SQL and ODBC. For a list of possible values, see Appendix A, Errors, Error Codes, and Common Problems.

SQLSTATE values returned by mysql_sqlstate() differ from MySQL-specific error numbers returned by mysql_errno(). For example, the mysql client program displays errors using the following format, where 1146 is the mysql_errno() value and '42S02' is the corresponding mysql_sqlstate() value:

shell> SELECT * FROM no_such_table;
ERROR 1146 (42S02): Table 'test.no_such_table' doesn't exist

Not all MySQL error numbers are mapped to SQLSTATE error codes. The value 'HY000' (general error) is used for unmapped error numbers.

If you call mysql_sqlstate() after mysql_real_connect() fails, mysql_sqlstate() might not return a useful value. For example, this happens if a host is blocked by the server and the connection is closed without any SQLSTATE value being sent to the client.

This function was added in MySQL 4.1.1.

Return Values

A null-terminated character string containing the SQLSTATE error code.

See Also

See Section 17.2.3.14, “mysql_errno(), Section 17.2.3.15, “mysql_error(), and Section 17.2.7.26, “mysql_stmt_sqlstate().

17.2.3.65. mysql_ssl_set()

my_bool mysql_ssl_set(MYSQL *mysql, const char *key, const char *cert, const char *ca, const char *capath, const char *cipher)

Description

mysql_ssl_set() is used for establishing secure connections using SSL. It must be called before mysql_real_connect().

mysql_ssl_set() does nothing unless OpenSSL support is enabled in the client library.

mysql is the connection handler returned from mysql_init(). The other parameters are specified as follows:

  • key is the pathname to the key file.

  • cert is the pathname to the certificate file.

  • ca is the pathname to the certificate authority file.

  • capath is the pathname to a directory that contains trusted SSL CA certificates in pem format.

  • cipher is a list of allowable ciphers to use for SSL encryption.

Any unused SSL parameters may be given as NULL.

Return Values

This function always returns 0. If SSL setup is incorrect, mysql_real_connect() returns an error when you attempt to connect.

17.2.3.66. mysql_stat()

const char *mysql_stat(MYSQL *mysql)

Description

Returns a character string containing information similar to that provided by the mysqladmin status command. This includes uptime in seconds and the number of running threads, questions, reloads, and open tables.

Return Values

A character string describing the server status. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

MYSQL_RES *mysql_store_result(MYSQL *mysql)

Description

After invoking mysql_query() or mysql_real_query(), you must call mysql_store_result() or mysql_use_result() for every statement that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN, CHECK TABLE, and so forth). You must also call mysql_free_result() after you are done with the result set.

You don't have to call mysql_store_result() or mysql_use_result() for other statements, but it does not do any harm or cause any notable performance degradation if you call mysql_store_result() in all cases. You can detect whether the statement has a result set by checking whether mysql_store_result() returns a non-zero value (more about this later on).

If you enable multiple-statement support, you should retrieve results from calls to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 17.2.9, “C API Handling of Multiple Statement Execution”.

If you want to know whether a statement should return a result set, you can use mysql_field_count() to check for this. See Section 17.2.3.22, “mysql_field_count().

mysql_store_result() reads the entire result of a query to the client, allocates a MYSQL_RES structure, and places the result into this structure.

mysql_store_result() returns a null pointer if the statement didn't return a result set (for example, if it was an INSERT statement).

mysql_store_result() also returns a null pointer if reading of the result set failed. You can check whether an error occurred by checking whether mysql_error() returns a non-empty string, mysql_errno() returns non-zero, or mysql_field_count() returns zero.

An empty result set is returned if there are no rows returned. (An empty result set differs from a null pointer as a return value.)

After you have called mysql_store_result() and gotten back a result that isn't a null pointer, you can call mysql_num_rows() to find out how many rows are in the result set.

You can call mysql_fetch_row() to fetch rows from the result set, or mysql_row_seek() and mysql_row_tell() to obtain or set the current row position within the result set.

See Section 17.2.14.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

A MYSQL_RES result structure with the results. NULL (0) if an error occurred.

Errors

mysql_store_result() resets mysql_error() and mysql_errno() if it succeeds.

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.3.68. mysql_thread_id()

unsigned long mysql_thread_id(MYSQL *mysql)

Description

Returns the thread ID of the current connection. This value can be used as an argument to mysql_kill() to kill the thread.

If the connection is lost and you reconnect with mysql_ping(), the thread ID changes. This means you should not get the thread ID and store it for later. You should get it when you need it.

Return Values

The thread ID of the current connection.

Errors

None.

17.2.3.69. mysql_use_result()

MYSQL_RES *mysql_use_result(MYSQL *mysql)

Description

You must call mysql_store_result() or mysql_use_result() for every query that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN).

mysql_use_result() initiates a result set retrieval but does not actually read the result set into the client like mysql_store_result() does. Instead, each row must be retrieved individually by making calls to mysql_fetch_row(). This reads the result of a query directly from the server without storing it in a temporary table or local buffer, which is somewhat faster and uses much less memory than mysql_store_result(). The client allocates memory only for the current row and a communication buffer that may grow up to max_allowed_packet bytes.

On the other hand, you shouldn't use mysql_use_result() if you are doing a lot of processing for each row on the client side, or if the output is sent to a screen on which the user may type a ^S (stop scroll). This ties up the server and prevent other threads from updating any tables from which the data is being fetched.

When using mysql_use_result(), you must execute mysql_fetch_row() until a NULL value is returned, otherwise, the unfetched rows are returned as part of the result set for your next query. The C API gives the error Commands out of sync; you can't run this command now if you forget to do this!

You may not use mysql_data_seek(), mysql_row_seek(), mysql_row_tell(), mysql_num_rows(), or mysql_affected_rows() with a result returned from mysql_use_result(), nor may you issue other queries until mysql_use_result() has finished. (However, after you have fetched all the rows, mysql_num_rows() accurately returns the number of rows fetched.)

You must call mysql_free_result() once you are done with the result set.

When using the libmysqld embedded server, the memory benefits are essentially lost because memory usage incrementally increases with each row retrieved until mysql_free_result() is called.

Return Values

A MYSQL_RES result structure. NULL if an error occurred.

Errors

mysql_use_result() resets mysql_error() and mysql_errno() if it succeeds.

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

unsigned int mysql_warning_count(MYSQL *mysql)

Description

Returns the number of warnings generated during execution of the previous SQL statement.

This function was added in MySQL 4.1.0.

Return Values

The warning count.

Errors

None.

17.2.4. C API Prepared Statements

As of MySQL 4.1, the client/server protocol provides for the use of prepared statements. This capability uses the MYSQL_STMT statement handler data structure returned by the mysql_stmt_init() initialization function. Prepared execution is an efficient way to execute a statement more than once. The statement is first parsed to prepare it for execution. Then it is executed one or more times at a later time, using the statement handle returned by the initialization function.

Prepared execution is faster than direct execution for statements executed more than once, primarily because the query is parsed only once. In the case of direct execution, the query is parsed every time it is executed. Prepared execution also can provide a reduction of network traffic because for each execution of the prepared statement, it is necessary only to send the data for the parameters.

Prepared statements might not provide a performance increase in some situations. For best results, test your application both with prepared and non-prepared statements and choose whichever yields best performance.

Another advantage of prepared statements is that it uses a binary protocol that makes data transfer between client and server more efficient.

The following statements can be used as prepared statements: CREATE TABLE, DELETE, DO, INSERT, REPLACE, SELECT, SET, UPDATE, and most SHOW statements. Other statements are not yet supported.

MySQL Enterprise MySQL Enterprise subscribers will find more information about using prepared statements in the Knowledge Base article, How can I create server-side prepared statements?. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.

17.2.5. C API Prepared Statement Data types

Note

Some incompatible changes were made in MySQL 4.1.2. See Section 17.2.7, “C API Prepared Statement Function Descriptions”, for details.

Prepared statements use several data structures:

  • To prepare a statement, pass the statement string to mysql_stmt_init(), which returns a pointer to a MYSQL_STMT data structure.

  • To provide input parameters for a prepared statement, set up MYSQL_BIND structures and pass them to mysql_stmt_bind_param(). To receive output column values, set up MYSQL_BIND structures and pass them to mysql_stmt_bind_result().

  • The MYSQL_TIME structure is used to transfer temporal data in both directions.

The following discussion describes the prepared statement data types in detail.

  • MYSQL_STMT

    This structure represents a prepared statement. A statement is created by calling mysql_stmt_init(), which returns a statement handle (that is, a pointer to a MYSQL_STMT). The handle is used for all subsequent operations with the statement until you close it with mysql_stmt_close(), at which point the handle becomes invalid.

    The MYSQL_STMT structure has no members that are intended for application use. Also, you should not try to make a copy of a MYSQL_STMT structure. There is no guarantee that such a copy will be usable.

    Multiple statement handles can be associated with a single connection. The limit on the number of handles depends on the available system resources.

  • MYSQL_BIND

    This structure is used both for statement input (data values sent to the server) and output (result values returned from the server):

    To use a MYSQL_BIND structure, you should zero its contents to initialize it, and then set its members appropriately. For example, to declare and initialize an array of three MYSQL_BIND structures, use this code:

    MYSQL_BIND bind[3];
    memset(bind, 0, sizeof(bind));
    

    The MYSQL_BIND structure contains the following members for use by application programs. For several of the members, the manner of use depends on whether the structure is used for input or output.

    • enum enum_field_types buffer_type

      The type of the buffer. This member indicates the data type of the C language variable that you are binding to the statement parameter. The allowable buffer_type values are listed later in this section. For input, buffer_type indicates the type of the variable containing the value that you will send to the server. For output, it indicates the type of the variable into which you want a value received from the server to be stored.

    • void *buffer

      A pointer to the buffer to be used for data transfer. This is the address of a variable.

      For input, buffer is a pointer to the variable in which a statement parameter's data value is stored. When you call mysql_stmt_execute(), MySQL takes the value that you have stored in the variable and uses it in place of the corresponding parameter marker in the statement.

      For output, buffer is a pointer to the variable in which to return a result set column value. When you call mysql_stmt_fetch(), MySQL returns a column value and stores it in this variable. You can access the value when the call returns.

      To minimize the need for MySQL to perform type conversions between C language values on the client side and SQL values on the server side, use variables that have types similar to those of the corresponding SQL values. For numeric data types, buffer should point to a variable of the proper numeric C type. (For char or integer variables, you should also indicate whether the variable has the unsigned attribute by setting the is_unsigned member, described later in this list.) For character (non-binary) and binary string data types, buffer should point to a character buffer. For date and time data types, buffer should point to a MYSQL_TIME structure.

      See the notes about type conversions later in the section.

    • unsigned long buffer_length

      The actual size of *buffer in bytes. This indicates the maximum amount of data that can be stored in the buffer. For character and binary C data, the buffer_length value specifies the length of *buffer when used with mysql_stmt_bind_param() to specify input values, or the maximum number of output data bytes that can be fetched into the buffer when used with mysql_stmt_bind_result().

    • unsigned long *length

      A pointer to an unsigned long variable that indicates the actual number of bytes of data stored in *buffer. length is used for character or binary C data.

      For input parameter data binding, length points to an unsigned long variable that indicates the actual length of the parameter value stored in *buffer; this is used by mysql_stmt_execute().

      For output value binding, the return value of mysql_stmt_fetch() determines the interpretation of the length:

      • If mysql_stmt_fetch() returns 0, *length indicates the actual length of the parameter value.

      • If mysql_stmt_fetch() returns MYSQL_DATA_TRUNCATED, *length indicates the non-truncated length of the parameter value. In this case, the minimum of *length and buffer_length indicates the actual length of the value.

      length is ignored for numeric and temporal data types because the length of the data value is determined by the buffer_type value.

      If you need to be able to determine the length of a returned value before fetching it with mysql_stmt_fetch(), see Section 17.2.7.11, “mysql_stmt_fetch(), for some strategies.

    • my_bool *is_null

      This member points to a my_bool variable that is true if a value is NULL, false if it is not NULL. For input, set *is_null to true to indicate that you are passing a NULL value as a statement parameter.

      The reason that is_null is not a boolean scalar but is instead a pointer to a boolean scalar is to provide flexibility in how you specify NULL values:

      • If your data values are always NULL, use MYSQL_TYPE_NULL as the buffer_type value when you bind the column. The other members do not matter.

      • If your data values are always NOT NULL, set the other members appropriately for the variable you are binding, and set is_null = (my_bool*) 0.

      • In all other cases, set the other members appriopriately, and set is_null to the address of a my_bool variable. Set that variable's value to true or false appropriately between executions to indicate whether data values are NULL or NOT NULL, respectively.

      For output, the value pointed to by is_null is set to true after you fetch a row if the result set column value returned from the statement is NULL.

    • my_bool is_unsigned

      This member is used for C variables with data types that can be unsigned (char, short int, int, long long int). Set is_unsigned to true if the variable pointed to by buffer is unsigned and false otherwise. For example, if you bind a signed char variable to buffer, specify a type code of MYSQL_TYPE_TINY and set is_unsigned to false. If you bind an unsigned char instead, the type code is the same but is_unsigned should be true. (For char, it is not defined whether it is signed or unsigned, so it is best to be explicit about signedness by using signed char or unsigned char.)

      is_unsigned applies only to the C language variable on the client side. It indicates nothing about the signedness of the corresponding SQL value on the server side. For example, if you use an int variable to supply a value for a BIGINT UNSIGNED column, is_unsigned should be false because int is a signed type. If you use an unsigned int variable to supply a value for a BIGINT column, is_unsigned should be true because unsigned int is an unsigned type. MySQL performs the proper conversion between signed and unsigned values in both directions, although a warning occurs if truncation results.

  • MYSQL_TIME

    This structure is used to send and receive DATE, TIME, DATETIME, and TIMESTAMP data directly to and from the server. Set the buffer_type member of a MYSQL_BIND structure to one of the temporal types (MYSQL_TYPE_TIME, MYSQL_TYPE_DATE, MYSQL_TYPE_DATETIME, MYSQL_TYPE_TIMESTAMP), and set the buffer member to point to a MYSQL_TIME structure.

    The MYSQL_TIME structure contains the members listed in the following table.

    MemberDescription
    unsigned int yearThe year
    unsigned int monthThe month of the year
    unsigned int dayThe day of the month
    unsigned int hourThe hour of the day
    unsigned int minuteThe minute of the hour
    unsigned int secondThe second of the minute
    my_bool negA boolean flag to indicate whether the time is negative
    unsigned long second_partThe fractional part of the second in microseconds; currently unused

    Only those parts of a MYSQL_TIME structure that apply to a given type of temporal value are used. The year, month, and day elements are used for DATE, DATETIME, and TIMESTAMP values. The hour, minute, and second elements are used for TIME, DATETIME, and TIMESTAMP values. See Section 17.2.10, “C API Handling of Date and Time Values”.

The following table shows the allowable values that may be specified in the buffer_type member of MYSQL_BIND structures for input values. The value should be chosen according to the data type of the C language variable that you are binding. If the variable is unsigned, you should also set the is_unsigned member to true. The table shows the C variable types that you can use, the corresponding type codes, and the SQL data types for which the supplied value can be used without conversion.

Input Variable C Typebuffer_type ValueSQL Type of Destination Value
signed charMYSQL_TYPE_TINYTINYINT
short intMYSQL_TYPE_SHORTSMALLINT
intMYSQL_TYPE_LONGINT
long long intMYSQL_TYPE_LONGLONGBIGINT
floatMYSQL_TYPE_FLOATFLOAT
doubleMYSQL_TYPE_DOUBLEDOUBLE
MYSQL_TIMEMYSQL_TYPE_TIMETIME
MYSQL_TIMEMYSQL_TYPE_DATEDATE
MYSQL_TIMEMYSQL_TYPE_DATETIMEDATETIME
MYSQL_TIMEMYSQL_TYPE_TIMESTAMPTIMESTAMP
char[]MYSQL_TYPE_STRING (for non-binary data)TEXT, CHAR, VARCHAR
char[]MYSQL_TYPE_BLOB (for binary data)BLOB, BINARY, VARBINARY
 MYSQL_TYPE_NULLNULL

The use of MYSQL_TYPE_NULL is described earlier in connection with the is_null member.

The following table shows the allowable values that may be specified in the buffer_type member of MYSQL_BIND structures for output values. The value should be chosen according to the data type of the C language variable that you are binding. If the variable is unsigned, you should also set the is_unsigned member to true. The table shows the SQL types of received values, the corresponding type code that such values have in result set metadata, and the recommended C language data types to bind to the MYSQL_BIND structure to receive the SQL values without conversion.

If there is a mismatch between the C variable type on the client side and the corresponding SQL value on the server side, MySQL performs implicit type conversions in both directions.

SQL Type of Received Valuebuffer_type ValueOutput Variable C Type
TINYINTMYSQL_TYPE_TINYsigned char
SMALLINTMYSQL_TYPE_SHORTshort int
MEDIUMINTMYSQL_TYPE_INT24int
INTMYSQL_TYPE_LONGint
BIGINTMYSQL_TYPE_LONGLONGlong long int
FLOATMYSQL_TYPE_FLOATfloat
DOUBLEMYSQL_TYPE_DOUBLEdouble
YEARMYSQL_TYPE_SHORTshort int
TIMEMYSQL_TYPE_TIMEMYSQL_TIME
DATEMYSQL_TYPE_DATEMYSQL_TIME
DATETIMEMYSQL_TYPE_DATETIMEMYSQL_TIME
TIMESTAMPMYSQL_TYPE_TIMESTAMPMYSQL_TIME
CHAR, BINARYMYSQL_TYPE_STRINGchar[]
VARCHAR, VARBINARYMYSQL_TYPE_VAR_STRINGchar[]
TINYBLOB, TINYTEXTMYSQL_TYPE_TINY_BLOBchar[]
BLOB, TEXTMYSQL_TYPE_BLOBchar[]
MEDIUMBLOB, MEDIUMTEXTMYSQL_TYPE_MEDIUM_BLOBchar[]
LONGBLOB, LONGTEXTMYSQL_TYPE_LONG_BLOBchar[]

MySQL knows the type code for the SQL value on the server side. The buffer_type value indicates the MySQL the type code of the C variable that holds the value on the client side. The two codes together tell MySQL what conversion must be performed, if any. Here are some examples:

  • If you use MYSQL_TYPE_LONG with an int variable to pass an integer value to the server that is to be stored into a FLOAT column, MySQL converts the value to floating-point format before storing it.

  • If you fetch a SQL MEDIUMINT column value, but specify a buffer_type value of MYSQL_TYPE_LONGLONG and use a C variable of type long long int as the destination buffer, MySQL will convert the MEDIUMINT value (which requires less than 8 bytes) for storage into the long long int (an 8-byte variable).

  • If you fetch a numeric column with a value of 255 into a char[4] character array and specify a buffer_type value of MYSQL_TYPE_STRING, the resulting value in the array will be a 4-byte string containing '255\0'.

  • DECIMAL values are returned as strings, which is why the corresponding C type is char[]. DECIMAL values returned by the server correspond to the string representation of the original server-side value. For example, 12.345 is returned to the client as '12.345'. If you specify MYSQL_TYPE_NEWDECIMAL and bind a string buffer to the MYSQL_BIND structure, mysql_stmt_fetch() stores the value in the buffer without conversion. If instead you specify a numeric variable and type code, mysql_stmt_fetch() converts the string-format DECIMAL value to numeric form.

  • For the MYSQL_TYPE_BIT type code, BIT values are returned into a string buffer (thus, the corresponding C type is char[] here, too). The value represents a bit string that requires interpretation on the client side. To return the value as a type that is easier to deal with, you can cause the value to be cast to integer using either of the following types of expressions:

    SELECT bit_col + 0 FROM t
    SELECT CAST(bit_col AS UNSIGNED) FROM t
    

    To retrieve the value, bind an integer variable large enough to hold the value and specify the appropriate corresponding integer type code.

Before binding variables to the MYSQL_BIND structures that are to be used for fetching column values, you can check the type codes for each column of the result set. This might be desirable if you want to determine which variable types would be best to use to avoid type conversions. To get the type codes, call mysql_stmt_result_metadata() after executing the prepared statement with mysql_stmt_execute(). The metadata provides access to the type codes for the result set as described in Section 17.2.7.22, “mysql_stmt_result_metadata(), and Section 17.2.1, “C API Data Types”.

If you cause the max_length member of the MYSQL_FIELD column metadata structures to be set (by calling mysql_stmt_attr_set()), be aware that the max_length values for the result set indicate the lengths of the longest string representation of the result values, not the lengths of the binary representation. That is, max_length does not necessarily correspond to the size of the buffers needed to fetch the values with the binary protocol used for prepared statements. The size of the buffers should be chosen according to the types of the variables into which you fetch the values.

For input character (non-binary) string data (indicated by MYSQL_TYPE_STRING), the value is assumed to be in the character set indicated by the character_set_client system variable. If the value is stored into a column with a different character set, the appropriate conversion to that character set occurs. For input binary string data (indicated by MYSQL_TYPE_BLOB), the value is treated as having the binary character set; that is, it is treated as a byte string and no conversion occurs.

To determine whether output string values in a result set returned from the server contain binary or non-binary data, check whether the charsetnr value of the result set metadata is 63 (see Section 17.2.1, “C API Data Types”). If so, the character set is binary, which indicates binary rather than non-binary data. This enables you to distinguish BINARY from CHAR, VARBINARY from VARCHAR, and the BLOB types from the TEXT types.

17.2.6. C API Prepared Statement Function Overview

Note

Some incompatible changes were made in MySQL 4.1.2. See Section 17.2.7, “C API Prepared Statement Function Descriptions”, for details.

The functions available for prepared statement processing are summarized here and described in greater detail in a later section. See Section 17.2.7, “C API Prepared Statement Function Descriptions”.

FunctionDescription
mysql_stmt_affected_rows()Returns the number of rows changed, deleted, or inserted by prepared UPDATE, DELETE, or INSERT statement
mysql_stmt_attr_get()Get value of an attribute for a prepared statement
mysql_stmt_attr_set()Sets an attribute for a prepared statement
mysql_stmt_bind_param()Associates application data buffers with the parameter markers in a prepared SQL statement
mysql_stmt_bind_result()Associates application data buffers with columns in the result set
mysql_stmt_close()Frees memory used by prepared statement
mysql_stmt_data_seek()Seeks to an arbitrary row number in a statement result set
mysql_stmt_errno()Returns the error number for the last statement execution
mysql_stmt_error()Returns the error message for the last statement execution
mysql_stmt_execute()Executes the prepared statement
mysql_stmt_fetch()Fetches the next row of data from the result set and returns data for all bound columns
mysql_stmt_fetch_column()Fetch data for one column of the current row of the result set
mysql_stmt_field_count()Returns the number of result columns for the most recent statement
mysql_stmt_free_result()Free the resources allocated to the statement handle
mysql_stmt_init()Allocates memory for MYSQL_STMT structure and initializes it
mysql_stmt_insert_id()Returns the ID generated for an AUTO_INCREMENT column by prepared statement
mysql_stmt_num_rows()Returns total row count from the buffered statement result set
mysql_stmt_param_count()Returns the number of parameters in a prepared SQL statement
mysql_stmt_param_metadata()(Return parameter metadata in the form of a result set.) Currently, this function does nothing
mysql_stmt_prepare()Prepares an SQL string for execution
mysql_stmt_reset()Reset the statement buffers in the server
mysql_stmt_result_metadata()Returns prepared statement metadata in the form of a result set
mysql_stmt_row_seek()Seeks to a row offset in a statement result set, using value returned from mysql_stmt_row_tell()
mysql_stmt_row_tell()Returns the statement row cursor position
mysql_stmt_send_long_data()Sends long data in chunks to server
mysql_stmt_sqlstate()Returns the SQLSTATE error code for the last statement execution
mysql_stmt_store_result()Retrieves the complete result set to the client

Call mysql_stmt_init() to create a statement handle, then mysql_stmt_prepare() to prepare it, mysql_stmt_bind_param() to supply the parameter data, and mysql_stmt_execute() to execute the statement. You can repeat the mysql_stmt_execute() by changing parameter values in the respective buffers supplied through mysql_stmt_bind_param().

If the statement is a SELECT or any other statement that produces a result set, mysql_stmt_prepare() also returns the result set metadata information in the form of a MYSQL_RES result set through mysql_stmt_result_metadata().

You can supply the result buffers using mysql_stmt_bind_result(), so that the mysql_stmt_fetch() automatically returns data to these buffers. This is row-by-row fetching.

You can also send the text or binary data in chunks to server using mysql_stmt_send_long_data(). See Section 17.2.7.25, “mysql_stmt_send_long_data().

When statement execution has been completed, the statement handle must be closed using mysql_stmt_close() so that all resources associated with it can be freed.

If you obtained a SELECT statement's result set metadata by calling mysql_stmt_result_metadata(), you should also free the metadata using mysql_free_result().

Execution Steps

To prepare and execute a statement, an application follows these steps:

  1. Create a prepared statement handle with mysql_stmt_init(). To prepare the statement on the server, call mysql_stmt_prepare() and pass it a string containing the SQL statement.

  2. If the statement produces a result set, call mysql_stmt_result_metadata() to obtain the result set metadata. This metadata is itself in the form of result set, albeit a separate one from the one that contains the rows returned by the query. The metadata result set indicates how many columns are in the result and contains information about each column.

  3. Set the values of any parameters using mysql_stmt_bind_param(). All parameters must be set. Otherwise, statement execution returns an error or produces unexpected results.

  4. Call mysql_stmt_execute() to execute the statement.

  5. If the statement produces a result set, bind the data buffers to use for retrieving the row values by calling mysql_stmt_bind_result().

  6. Fetch the data into the buffers row by row by calling mysql_stmt_fetch() repeatedly until no more rows are found.

  7. Repeat steps 3 through 6 as necessary, by changing the parameter values and re-executing the statement.

When mysql_stmt_prepare() is called, the MySQL client/server protocol performs these actions:

  • The server parses the statement and sends the okay status back to the client by assigning a statement ID. It also sends total number of parameters, a column count, and its metadata if it is a result set oriented statement. All syntax and semantics of the statement are checked by the server during this call.

  • The client uses this statement ID for the further operations, so that the server can identify the statement from among its pool of statements.

When mysql_stmt_execute() is called, the MySQL client/server protocol performs these actions:

  • The client uses the statement handle and sends the parameter data to the server.

  • The server identifies the statement using the ID provided by the client, replaces the parameter markers with the newly supplied data, and executes the statement. If the statement produces a result set, the server sends the data back to the client. Otherwise, it sends an okay status and total number of rows changed, deleted, or inserted.

When mysql_stmt_fetch() is called, the MySQL client/server protocol performs these actions:

  • The client reads the data from the packet row by row and places it into the application data buffers by doing the necessary conversions. If the application buffer type is same as that of the field type returned from the server, the conversions are straightforward.

If an error occurs, you can get the statement error code, error message, and SQLSTATE value using mysql_stmt_errno(), mysql_stmt_error(), and mysql_stmt_sqlstate(), respectively.

Prepared Statement Logging

For prepared statements that are executed with the mysql_stmt_prepare() and mysql_stmt_execute() C API functions, the server writes Prepare and Execute lines to the general query log so that you can tell when statements are prepared and executed.

Suppose that you prepare and execute a statement as follows:

  1. Call mysql_stmt_prepare() to prepare the statement string "SELECT ?".

  2. Call mysql_stmt_bind_param() to bind the value 3 to the parameter in the prepared statement.

  3. Call mysql_stmt_execute() to execute the prepared statement.

As a result of the preceding calls, the server writes the following lines to the general query log:

Prepare  [1] SELECT ?
Execute  [1] SELECT 3

Each Prepare and Execute line in the log is tagged with a [N] statement identifier so that you can keep track of which prepared statement is being logged. N is a positive integer. If there are multiple prepared statements active simultaneously for the client, N may be greater than 1. Each Execute lines shows a prepared statement after substitution of data values for ? parameters.

Version notes: Prepare lines are displayed without [N] before MySQL 4.1.10. Execute lines are not displayed at all before MySQL 4.1.10.

17.2.7. C API Prepared Statement Function Descriptions

To prepare and execute queries, use the functions described in detail in the following sections.

Note

In MySQL 4.1.2, the names of several prepared statement functions were changed, as shown here:

Old NameNew Name
mysql_bind_param()mysql_stmt_bind_param()
mysql_bind_result()mysql_stmt_bind_result()
mysql_prepare()mysql_stmt_prepare()
mysql_execute()mysql_stmt_execute()
mysql_fetch()mysql_stmt_fetch()
mysql_fetch_column()mysql_stmt_fetch_column()
mysql_param_count()mysql_stmt_param_count()
mysql_param_result()mysql_stmt_param_metadata()
mysql_get_metadata()mysql_stmt_result_metadata()
mysql_send_long_data()mysql_stmt_send_long_data()

All functions that operate with a MYSQL_STMT structure begin with the prefix mysql_stmt_.

Also in 4.1.2, the signature of the mysql_stmt_prepare() function was changed to int mysql_stmt_prepare(MYSQL_STMT *stmt, const char *query, unsigned long length). To create a MYSQL_STMT handle, you should use the mysql_stmt_init() function.

my_ulonglong mysql_stmt_affected_rows(MYSQL_STMT *stmt)

Description

Returns the total number of rows changed, deleted, or inserted by the last executed statement. May be called immediately after mysql_stmt_execute() for UPDATE, DELETE, or INSERT statements. For SELECT statements, mysql_stmt_affected_rows() works like mysql_num_rows().

This function was added in MySQL 4.1.0.

Return Values

An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records were updated for an UPDATE statement, no rows matched the WHERE clause in the query, or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_stmt_affected_rows() was called prior to calling mysql_stmt_store_result(). Because mysql_stmt_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

See Section 17.2.3.1, “mysql_affected_rows(), for additional information on the return value.

Errors

None.

Example

For the usage of mysql_stmt_affected_rows(), refer to the Example from Section 17.2.7.10, “mysql_stmt_execute().

my_bool mysql_stmt_attr_get(MYSQL_STMT *stmt, enum enum_stmt_attr_type option, void *arg)

Description

Can be used to get the current value for a statement attribute.

The option argument is the option that you want to get; the arg should point to a variable that should contain the option value. If the option is an integer, then arg should point to the value of the integer.

See Section 17.2.7.3, “mysql_stmt_attr_set(), for a list of options and option types.

Note

In MySQL 4.1, mysql_stmt_attr_get() uses unsigned int *, not my_bool *, for STMT_ATTR_UPDATE_MAX_LENGTH. This is corrected in MySQL 5.1.7.

This function was added in MySQL 4.1.2.

Return Values

Zero if successful. Non-zero if option is unknown.

Errors

None.

my_bool mysql_stmt_attr_set(MYSQL_STMT *stmt, enum enum_stmt_attr_type option, const void *arg)

Description

Can be used to affect behavior for a prepared statement. In MySQL 4.1, the option argument can take the single value STMT_ATTR_UPDATE_MAX_LENGTH; the arg argument is a pointer of type my_bool *. If arg points to the value 1, then the metadata MYSQL_FIELD->max_length in mysql_stmt_store_result() is updated when the prepared statement is executed.

Note

In MySQL 4.1, mysql_stmt_attr_get() uses unsigned int *, not my_bool *, for STMT_ATTR_UPDATE_MAX_LENGTH. This is corrected in MySQL 5.1.7.

This function was added in MySQL 4.1.2. Additional options are planned for this function in later versions of MySQL.

Return Values

Zero if successful. Non-zero if option is unknown.

Errors

None.

my_bool mysql_stmt_bind_param(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_param() is used to bind input data for the parameter markers in the SQL statement that was passed to mysql_stmt_prepare(). It uses MYSQL_BIND structures to supply the data. bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain one element for each “?” parameter marker that is present in the query.

Suppose that you prepare the following statement:

INSERT INTO mytbl VALUES(?,?,?)

When you bind the parameters, the array of MYSQL_BIND structures must contain three elements, and can be declared like this:

MYSQL_BIND bind[3];

Section 17.2.5, “C API Prepared Statement Data types”, describes the members of each MYSQL_BIND element and how they should be set to provide input values.

This function was added in MySQL 4.1.2.

Return Values

Zero if the bind operation was successful. Non-zero if an error occurred.

Errors

  • CR_UNSUPPORTED_PARAM_TYPE

    The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_bind_param(), refer to the Example from Section 17.2.7.10, “mysql_stmt_execute().

my_bool mysql_stmt_bind_result(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_result() is used to associate (that is, bind) output columns in the result set to data buffers and length buffers. When mysql_stmt_fetch() is called to fetch data, the MySQL client/server protocol places the data for the bound columns into the specified buffers.

All columns must be bound to buffers prior to calling mysql_stmt_fetch(). bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain one element for each column of the result set. If you do not bind columns to MYSQL_BIND structures, mysql_stmt_fetch() simply ignores the data fetch. The buffers should be large enough to hold the data values, because the protocol doesn't return data values in chunks.

A column can be bound or rebound at any time, even after a result set has been partially retrieved. The new binding takes effect the next time mysql_stmt_fetch() is called. Suppose that an application binds the columns in a result set and calls mysql_stmt_fetch(). The client/server protocol returns data in the bound buffers. Then suppose that the application binds the columns to a different set of buffers. The protocol places data into the newly bound buffers when the next call to mysql_stmt_fetch() occurs.

To bind a column, an application calls mysql_stmt_bind_result() and passes the type, address, and length of the output buffer into which the value should be stored. Section 17.2.5, “C API Prepared Statement Data types”, describes the members of each MYSQL_BIND element and how they should be set to receive output values.

This function was added in MySQL 4.1.2.

Return Values

Zero if the bind operation was successful. Non-zero if an error occurred.

Errors

  • CR_UNSUPPORTED_PARAM_TYPE

    The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_bind_result(), refer to the Example from Section 17.2.7.11, “mysql_stmt_fetch().

my_bool mysql_stmt_close(MYSQL_STMT *)

Description

Closes the prepared statement. mysql_stmt_close() also deallocates the statement handle pointed to by stmt.

If the current statement has pending or unread results, this function cancels them so that the next query can be executed.

This function was added in MySQL 4.1.0.

Return Values

Zero if the statement was freed successfully. Non-zero if an error occurred.

Errors

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_close(), refer to the Example from Section 17.2.7.10, “mysql_stmt_execute().

void mysql_stmt_data_seek(MYSQL_STMT *stmt, my_ulonglong offset)

Description

Seeks to an arbitrary row in a statement result set. The offset value is a row number and should be in the range from 0 to mysql_stmt_num_rows(stmt)-1.

This function requires that the statement result set structure contains the entire result of the last executed query, so mysql_stmt_data_seek() may be used only in conjunction with mysql_stmt_store_result().

This function was added in MySQL 4.1.1.

Return Values

None.

Errors

None.

unsigned int mysql_stmt_errno(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_errno() returns the error code for the most recently invoked statement API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. Errors also are listed at Appendix A, Errors, Error Codes, and Common Problems.

This function was added in MySQL 4.1.0.

Return Values

An error code value. Zero if no error occurred.

Errors

None.

const char *mysql_stmt_error(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_error() returns a null-terminated string containing the error message for the most recently invoked statement API function that can succeed or fail. An empty string ("") is returned if no error occurred. This means the following two tests are equivalent:

if(*mysql_stmt_errno(stmt))
{
  // an error occurred
}

if (mysql_stmt_error(stmt)[0])
{
  // an error occurred
}

The language of the client error messages may be changed by recompiling the MySQL client library. Currently, you can choose error messages in several different languages.

This function was added in MySQL 4.1.0.

Return Values

A character string that describes the error. An empty string if no error occurred.

Errors

None.

int mysql_stmt_execute(MYSQL_STMT *stmt)

Description

mysql_stmt_execute() executes the prepared query associated with the statement handle. The currently bound parameter marker values are sent to server during this call, and the server replaces the markers with this newly supplied data.

If the statement is an UPDATE, DELETE, or INSERT, the total number of changed, deleted, or inserted rows can be found by calling mysql_stmt_affected_rows(). If this is a statement such as SELECT that generates a result set, you must call mysql_stmt_fetch() to fetch the data prior to calling any other functions that result in query processing. For more information on how to fetch the results, refer to Section 17.2.7.11, “mysql_stmt_fetch().

For statements that generate a result set, you can request that mysql_stmt_execute() open a cursor for the statement by calling mysql_stmt_attr_set() before executing the statement. If you execute a statement multiple times, mysql_stmt_execute() closes any open cursor before opening a new one.

This function was added in MySQL 4.1.2.

Return Values

Zero if execution was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

The following example demonstrates how to create and populate a table using mysql_stmt_init(), mysql_stmt_prepare(), mysql_stmt_param_count(), mysql_stmt_bind_param(), mysql_stmt_execute(), and mysql_stmt_affected_rows(). The mysql variable is assumed to be a valid connection handle.

#define STRING_SIZE 50

#define DROP_SAMPLE_TABLE "DROP TABLE IF EXISTS test_table"
#define CREATE_SAMPLE_TABLE "CREATE TABLE test_table(col1 INT,\
                                                 col2 VARCHAR(40),\
                                                 col3 SMALLINT,\
                                                 col4 TIMESTAMP)"
#define INSERT_SAMPLE "INSERT INTO \ 
                       test_table(col1,col2,col3) \
                       VALUES(?,?,?)"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[3];
my_ulonglong  affected_rows;
int           param_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
unsigned long str_length;
my_bool       is_null;

if (mysql_query(mysql, DROP_SAMPLE_TABLE))
{
  fprintf(stderr, " DROP TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

if (mysql_query(mysql, CREATE_SAMPLE_TABLE))
{
  fprintf(stderr, " CREATE TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

/* Prepare an INSERT query with 3 parameters */
/* (the TIMESTAMP column is not named; the server */
/*  sets it to the current date and time) */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, INSERT_SAMPLE, strlen(INSERT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), INSERT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, INSERT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in INSERT: %d\n", param_count);

if (param_count != 3) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Bind the data for all 3 parameters */

memset(bind, 0, sizeof(bind));

/* INTEGER PARAM */
/* This is a number type, so there is no need 
   to specify buffer_length */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= 0;
bind[0].length= 0;

/* STRING PARAM */
bind[1].buffer_type= MYSQL_TYPE_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= 0;
bind[1].length= &str_length;

/* SMALLINT PARAM */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;
bind[2].is_null= &is_null;
bind[2].length= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_param() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Specify the data values for the first row */
int_data= 10;             /* integer */
strncpy(str_data, "MySQL", STRING_SIZE); /* string  */
str_length= strlen(str_data);

/* INSERT SMALLINT data as NULL */
is_null= 1;

/* Execute the INSERT statement - 1*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), 1 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get the total number of affected rows */
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 1): %lu\n",
                (unsigned long) affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Specify data values for second row, 
   then re-execute the statement */
int_data= 1000;
strncpy(str_data, "
        The most popular Open Source database", 
        STRING_SIZE);
str_length= strlen(str_data);
small_data= 1000;         /* smallint */
is_null= 0;               /* reset */

/* Execute the INSERT statement - 2*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute, 2 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get the total rows affected */
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 2): %lu\n",
                (unsigned long) affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Close the statement */
if (mysql_stmt_close(stmt))
{
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

Note

For complete examples on the use of prepared statement functions, refer to the file tests/mysql_client_test.c. This file can be obtained from a MySQL source distribution or from the Bazaar source repository.

17.2.7.11. mysql_stmt_fetch()

int mysql_stmt_fetch(MYSQL_STMT *stmt)

Description

mysql_stmt_fetch() returns the next row in the result set. It can be called only while the result set exists; that is, after a call to mysql_stmt_execute() for a statement such as SELECT that creates a result set.

mysql_stmt_fetch() returns row data using the buffers bound by mysql_stmt_bind_result(). It returns the data in those buffers for all the columns in the current row set and the lengths are returned to the length pointer. All columns must be bound by the application before it calls mysql_stmt_fetch().

By default, result sets are fetched unbuffered a row at a time from the server. To buffer the entire result set on the client, call mysql_stmt_store_result() after binding the data buffers and before caling mysql_stmt_fetch().

If a fetched data value is a NULL value, the *is_null value of the corresponding MYSQL_BIND structure contains TRUE (1). Otherwise, the data and its length are returned in the *buffer and *length elements based on the buffer type specified by the application. Each numeric and temporal type has a fixed length, as listed in the following table. The length of the string types depends on the length of the actual data value, as indicated by data_length.

TypeLength
MYSQL_TYPE_TINY1
MYSQL_TYPE_SHORT2
MYSQL_TYPE_LONG4
MYSQL_TYPE_LONGLONG8
MYSQL_TYPE_FLOAT4
MYSQL_TYPE_DOUBLE8
MYSQL_TYPE_TIMEsizeof(MYSQL_TIME)
MYSQL_TYPE_DATEsizeof(MYSQL_TIME)
MYSQL_TYPE_DATETIMEsizeof(MYSQL_TIME)
MYSQL_TYPE_STRINGdata length
MYSQL_TYPE_BLOBdata_length

This function was added in MySQL 4.1.2.

Return Values

Return ValueDescription
0Successful, the data has been fetched to application data buffers.
1Error occurred. Error code and message can be obtained by calling mysql_stmt_errno() and mysql_stmt_error().
MYSQL_NO_DATANo more rows/data exists
MYSQL_DATA_TRUNCATEDData truncation occurred

MYSQL_DATA_TRUNCATED is not returned unless truncation reporting is enabled with mysql_options(). To determine which parameters were truncated when this value is returned, check the error members of the MYSQL_BIND parameter structures.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

  • CR_UNSUPPORTED_PARAM_TYPE

    The buffer type is MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, but the data type is not DATE, TIME, DATETIME, or TIMESTAMP.

  • All other unsupported conversion errors are returned from mysql_stmt_bind_result().

Example

The following example demonstrates how to fetch data from a table using mysql_stmt_result_metadata(), mysql_stmt_bind_result(), and mysql_stmt_fetch(). (This example expects to retrieve the two rows inserted by the example shown in Section 17.2.7.10, “mysql_stmt_execute().) The mysql variable is assumed to be a valid connection handle.

#define STRING_SIZE 50

#define SELECT_SAMPLE "SELECT col1, col2, col3, col4 \
                       FROM test_table"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[4];
MYSQL_RES     *prepare_meta_result;
MYSQL_TIME    ts;
unsigned long length[4];
int           param_count, column_count, row_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
my_bool       is_null[4];

/* Prepare a SELECT query to fetch data from test_table */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, SELECT_SAMPLE, strlen(SELECT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), SELECT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, SELECT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in SELECT: %d\n", param_count);

if (param_count != 0) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Fetch result set meta information */
prepare_meta_result = mysql_stmt_result_metadata(stmt);
if (!prepare_meta_result)
{
  fprintf(stderr,
         " mysql_stmt_result_metadata(), \ 
           returned no meta information\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get total columns in the query */
column_count= mysql_num_fields(prepare_meta_result);
fprintf(stdout, 
        " total columns in SELECT statement: %d\n", 
        column_count);

if (column_count != 4) /* validate column count */
{
  fprintf(stderr, " invalid column count returned by MySQL\n");
  exit(0);
}

/* Execute the SELECT query */
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Bind the result buffers for all 4 columns before fetching them */

memset(bind, 0, sizeof(bind));

/* INTEGER COLUMN */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= &is_null[0];
bind[0].length= &length[0];

/* STRING COLUMN */
bind[1].buffer_type= MYSQL_TYPE_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= &is_null[1];
bind[1].length= &length[1];

/* SMALLINT COLUMN */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;
bind[2].is_null= &is_null[2];
bind[2].length= &length[2];

/* TIMESTAMP COLUMN */
bind[3].buffer_type= MYSQL_TYPE_TIMESTAMP;
bind[3].buffer= (char *)&ts;
bind[3].is_null= &is_null[3];
bind[3].length= &length[3];

/* Bind the result buffers */
if (mysql_stmt_bind_result(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Now buffer all results to client (optional step) */
if (mysql_stmt_store_result(stmt))
{
  fprintf(stderr, " mysql_stmt_store_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Fetch all rows */
row_count= 0;
fprintf(stdout, "Fetching results ...\n");
while (!mysql_stmt_fetch(stmt))
{
  row_count++;
  fprintf(stdout, "  row %d\n", row_count);

  /* column 1 */
  fprintf(stdout, "   column1 (integer)  : ");
  if (is_null[0])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", int_data, length[0]);

  /* column 2 */
  fprintf(stdout, "   column2 (string)   : ");
  if (is_null[1])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %s(%ld)\n", str_data, length[1]);

  /* column 3 */
  fprintf(stdout, "   column3 (smallint) : ");
  if (is_null[2])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", small_data, length[2]);

  /* column 4 */
  fprintf(stdout, "   column4 (timestamp): ");
  if (is_null[3])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %04d-%02d-%02d %02d:%02d:%02d (%ld)\n",
                     ts.year, ts.month, ts.day,
                     ts.hour, ts.minute, ts.second,
                     length[3]);
  fprintf(stdout, "\n");
}

/* Validate rows fetched */
fprintf(stdout, " total rows fetched: %d\n", row_count);
if (row_count != 2)
{
  fprintf(stderr, " MySQL failed to return all rows\n");
  exit(0);
}

/* Free the prepared result metadata */
mysql_free_result(prepare_meta_result);


/* Close the statement */
if (mysql_stmt_close(stmt))
{
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

In some cases you might want to determine the length of a column value before fetching it with mysql_stmt_fetch(). For example, the value might be a long string or BLOB value for which you want to know how much space must be allocated. To accomplish this, you can use these strategies:

  • Before invoking mysql_stmt_fetch() to retrieve individual rows, invoke mysql_stmt_store_result() to buffer the entire result on the client side. Then the maximal length of column values will be indicated by the max_length member of the result set metadata returned by mysql_stmt_result_metadata(). This strategy requires that you pass STMT_ATTR_UPDATE_MAX_LENGTH to mysql_stmt_attr_set() or the max_length values will not be calculated.

  • Invoke mysql_stmt_fetch() with a zero-length buffer for the column in question and a pointer in which the real length can be stored. Then use the real length with mysql_stmt_fetch_column().

    real_length= 0;
    
    bind[0].buffer= 0;
    bind[0].buffer_length= 0;
    bind[0].length= &real_length
    mysql_stmt_bind_result(stmt, bind);
    
    mysql_stmt_fetch(stmt);
    if (real_length > 0)
    {
      data= malloc(real_length);
      bind[0].buffer= data;
      bind[0].buffer_length= real_length;
      mysql_stmt_fetch_column(stmt, 0, bind, 0);
    }
    

int mysql_stmt_fetch_column(MYSQL_STMT *stmt, MYSQL_BIND *bind, unsigned int column, unsigned long offset)

Description

Fetch one column from the current result set row. bind provides the buffer where data should be placed. It should be set up the same way as for mysql_stmt_bind_result(). column indicates which column to fetch. The first column is numbered 0. offset is the offset within the data value at which to begin retrieving data. This can be used for fetching the data value in pieces. The beginning of the value is offset 0.

This function was added in MySQL 4.1.2.

Return Values

Zero if the value was fetched successfully. Non-zero if an error occurred.

Errors

  • CR_INVALID_PARAMETER_NO

    Invalid column number.

  • CR_NO_DATA

    The end of the result set has already been reached.

unsigned int mysql_stmt_field_count(MYSQL_STMT *stmt)

Description

Returns the number of columns for the most recent statement for the statement handler. This value is zero for statements such as INSERT or DELETE that do not produce result sets.

mysql_stmt_field_count() can be called after you have prepared a statement by invoking mysql_stmt_prepare().

This function was added in MySQL 4.1.3.

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

my_bool mysql_stmt_free_result(MYSQL_STMT *stmt)

Description

Releases memory associated with the result set produced by execution of the prepared statement. If there is a cursor open for the statement, mysql_stmt_free_result() closes it.

This function was added in MySQL 4.1.1.

Return Values

Zero if the result set was freed successfully. Non-zero if an error occurred.

Errors

17.2.7.15. mysql_stmt_init()

MYSQL_STMT *mysql_stmt_init(MYSQL *mysql)

Description

Create a MYSQL_STMT handle. The handle should be freed with mysql_stmt_close(MYSQL_STMT *).

This function was added in MySQL 4.1.2.

Return values

A pointer to a MYSQL_STMT structure in case of success. NULL if out of memory.

Errors

  • CR_OUT_OF_MEMORY

    Out of memory.

my_ulonglong mysql_stmt_insert_id(MYSQL_STMT *stmt)

Description

Returns the value generated for an AUTO_INCREMENT column by the prepared INSERT or UPDATE statement. Use this function after you have executed prepared INSERT statement into a table which contains an AUTO_INCREMENT field.

See Section 17.2.3.35, “mysql_insert_id(), for more information.

This function was added in MySQL 4.1.2.

Return Values

Value for AUTO_INCREMENT column which was automatically generated or explicitly set during execution of prepared statement, or value generated by LAST_INSERT_ID(expr) function. Return value is undefined if statement does not set AUTO_INCREMENT value.

Errors

None.

my_ulonglong mysql_stmt_num_rows(MYSQL_STMT *stmt)

Description

Returns the number of rows in the result set.

The use of mysql_stmt_num_rows() depends on whether you used mysql_stmt_store_result() to buffer the entire result set in the statement handle.

If you use mysql_stmt_store_result(), mysql_stmt_num_rows() may be called immediately. Otherwise, the row count is unavailable unless you count the rows as you fetch them.

mysql_stmt_num_rows() is intended for use with statements that return a result set, such as SELECT. For statements such as INSERT, UPDATE, or DELETE, the number of affected rows can be obtained with mysql_stmt_affected_rows().

This function was added in MySQL 4.1.1.

Return Values

The number of rows in the result set.

Errors

None.

unsigned long mysql_stmt_param_count(MYSQL_STMT *stmt)

Description

Returns the number of parameter markers present in the prepared statement.

This function was added in MySQL 4.1.2.

Return Values

An unsigned long integer representing the number of parameters in a statement.

Errors

None.

Example

For the usage of mysql_stmt_param_count(), refer to the Example from Section 17.2.7.10, “mysql_stmt_execute().

MYSQL_RES *mysql_stmt_param_metadata(MYSQL_STMT *stmt)

This function currently does nothing.

This function was added in MySQL 4.1.2.

Description

Return Values

Errors

int mysql_stmt_prepare(MYSQL_STMT *stmt, const char *stmt_str, unsigned long length)

Description

Given the statement handle returned by mysql_stmt_init(), prepares the SQL statement pointed to by the string stmt_str and returns a status value. The string length should be given by the length argument. The string must consist of a single SQL statement. You should not add a terminating semicolon (“;”) or \g to the statement.

The application can include one or more parameter markers in the SQL statement by embedding question mark (“?”) characters into the SQL string at the appropriate positions.

The markers are legal only in certain places in SQL statements. For example, they are allowed in the VALUES() list of an INSERT statement (to specify column values for a row), or in a comparison with a column in a WHERE clause to specify a comparison value. However, they are not allowed for identifiers (such as table or column names), or to specify both operands of a binary operator such as the = equal sign. The latter restriction is necessary because it would be impossible to determine the parameter type. In general, parameters are legal only in Data Manipulation Language (DML) statements, and not in Data Definition Language (DDL) statements.

The parameter markers must be bound to application variables using mysql_stmt_bind_param() before executing the statement.

This function was added in MySQL 4.1.2.

Return Values

Zero if the statement was prepared successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

If the prepare operation was unsuccessful (that is, mysql_stmt_prepare() returns non-zero), the error message can be obtained by calling mysql_stmt_error().

Example

For the usage of mysql_stmt_prepare(), refer to the Example from Section 17.2.7.10, “mysql_stmt_execute().

17.2.7.21. mysql_stmt_reset()

my_bool mysql_stmt_reset(MYSQL_STMT *stmt)

Description

Reset the prepared statement on the client and server to state after prepare. This is mainly used to reset data sent with mysql_stmt_send_long_data(). Any open cursor for the statement is closed.

To re-prepare the statement with another query, use mysql_stmt_prepare().

This function was added in MySQL 4.1.1.

Return Values

Zero if the statement was reset successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

MYSQL_RES *mysql_stmt_result_metadata(MYSQL_STMT *stmt)

Description

If a statement passed to mysql_stmt_prepare() is one that produces a result set, mysql_stmt_result_metadata() returns the result set metadata in the form of a pointer to a MYSQL_RES structure that can be used to process the meta information such as total number of fields and individual field information. This result set pointer can be passed as an argument to any of the field-based API functions that process result set metadata, such as:

The result set structure should be freed when you are done with it, which you can do by passing it to mysql_free_result(). This is similar to the way you free a result set obtained from a call to mysql_store_result().

The result set returned by mysql_stmt_result_metadata() contains only metadata. It does not contain any row results. The rows are obtained by using the statement handle with mysql_stmt_fetch().

This function was added in MySQL 4.1.2.

Return Values

A MYSQL_RES result structure. NULL if no meta information exists for the prepared query.

Errors

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_result_metadata(), refer to the Example from Section 17.2.7.11, “mysql_stmt_fetch().

MYSQL_ROW_OFFSET mysql_stmt_row_seek(MYSQL_STMT *stmt, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a statement result set. The offset value is a row offset that should be a value returned from mysql_stmt_row_tell() or from mysql_stmt_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_stmt_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_stmt_row_seek() may be used only in conjunction with mysql_stmt_store_result().

This function was added in MySQL 4.1.1.

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_stmt_row_seek().

Errors

None.

MYSQL_ROW_OFFSET mysql_stmt_row_tell(MYSQL_STMT *stmt)

Description

Returns the current position of the row cursor for the last mysql_stmt_fetch(). This value can be used as an argument to mysql_stmt_row_seek().

You should use mysql_stmt_row_tell() only after mysql_stmt_store_result().

This function was added in MySQL 4.1.1.

Return Values

The current offset of the row cursor.

Errors

None.

my_bool mysql_stmt_send_long_data(MYSQL_STMT *stmt, unsigned int parameter_number, const char *data, unsigned long length)

Description

Allows an application to send parameter data to the server in pieces (or “chunks”). Call this function after mysql_stmt_bind_param() and before mysql_stmt_execute(). It can be called multiple times to send the parts of a character or binary data value for a column, which must be one of the TEXT or BLOB data types.

parameter_number indicates which parameter to associate the data with. Parameters are numbered beginning with 0. data is a pointer to a buffer containing data to be sent, and length indicates the number of bytes in the buffer.

Note

The next mysql_stmt_execute() call ignores the bind buffer for all parameters that have been used with mysql_stmt_send_long_data() since last mysql_stmt_execute() or mysql_stmt_reset().

If you want to reset/forget the sent data, you can do it with mysql_stmt_reset(). See Section 17.2.7.21, “mysql_stmt_reset().

This function was added in MySQL 4.1.2.

Return Values

Zero if the data is sent successfully to server. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

The following example demonstrates how to send the data for a TEXT column in chunks. It inserts the data value 'MySQL - The most popular Open Source database' into the text_column column. The mysql variable is assumed to be a valid connection handle.

#define INSERT_QUERY "INSERT INTO \
                      test_long_data(text_column) VALUES(?)"

MYSQL_BIND bind[1];
long       length;

stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, INSERT_QUERY, strlen(INSERT_QUERY)))
{
  fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}
 memset(bind, 0, sizeof(bind));
 bind[0].buffer_type= MYSQL_TYPE_STRING;
 bind[0].length= &length;
 bind[0].is_null= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, "\n param bind failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply data in chunks to server */
 if (mysql_stmt_send_long_data(stmt,0,"MySQL",5))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply the next piece of data */
 if (mysql_stmt_send_long_data(stmt,0,
           " - The most popular Open Source database",40))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Now, execute the query */
 if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, "\n mysql_stmt_execute failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

const char *mysql_stmt_sqlstate(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_sqlstate() returns a null-terminated string containing the SQLSTATE error code for the most recently invoked prepared statement API function that can succeed or fail. The error code consists of five characters. "00000" means “no error.” The values are specified by ANSI SQL and ODBC. For a list of possible values, see Appendix A, Errors, Error Codes, and Common Problems.

Note that not all MySQL errors are yet mapped to SQLSTATE codes. The value "HY000" (general error) is used for unmapped errors.

This function was added to MySQL 4.1.1.

Return Values

A null-terminated character string containing the SQLSTATE error code.

int mysql_stmt_store_result(MYSQL_STMT *stmt)

Description

Result sets are produced by executing prepared statements for SQL statements such as SELECT, SHOW, DESCRIBE, and EXPLAIN. By default, result sets for successfully executed prepared statements are not buffered on the client and mysql_stmt_fetch() fetches them one at a time from the server. To cause the complete result set to be buffered on the client, call mysql_stmt_store_result() after binding data buffers with mysql_stmt_bind_result() and before calling mysql_stmt_fetch() to fetch rows. (For an example, see Section 17.2.7.11, “mysql_stmt_fetch().)

mysql_stmt_store_result() is optional for result set processing, unless you will call mysql_stmt_data_seek(), mysql_stmt_row_seek(), or mysql_stmt_row_tell(). Those functions require a seekable result set.

It is unnecessary to call mysql_stmt_store_result() after executing a SQL statement that does not produce a result set, but if you do, it does not harm or cause any notable performance problem. You can detect whether the statement produced a result set by checking if mysql_stmt_result_metadata() returns NULL. For more information, refer to Section 17.2.7.22, “mysql_stmt_result_metadata().

Note

MySQL doesn't by default calculate MYSQL_FIELD->max_length for all columns in mysql_stmt_store_result() because calculating this would slow down mysql_stmt_store_result() considerably and most applications doesn't need max_length. If you want max_length to be updated, you can call mysql_stmt_attr_set(MYSQL_STMT, STMT_ATTR_UPDATE_MAX_LENGTH, &flag) to enable this. See Section 17.2.7.3, “mysql_stmt_attr_set().

This function was added in MySQL 4.1.0.

Return Values

Zero if the results are buffered successfully. Non-zero if an error occurred.

Errors

  • CR_INVALID_BUFFER_USE

    The parameter does not have a string or binary type.

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

17.2.8. C API Prepared Statement Problems

Here follows a list of the currently known problems with prepared statements:

  • TIME, TIMESTAMP, and DATETIME do not support parts of seconds (for example, from DATE_FORMAT()).

  • When converting an integer to string, ZEROFILL is honored with prepared statements in some cases where the MySQL server doesn't print the leading zeros. (For example, with MIN(number-with-zerofill)).

  • When converting a floating-point number to a string in the client, the rightmost digits of the converted value may differ slightly from those of the original value.

  • Prepared statements do not use the query cache, even in cases where a query does not contain any placeholders. See Section 7.5.3.1, “How the Query Cache Operates”.

17.2.9. C API Handling of Multiple Statement Execution

By default, mysql_query() and mysql_real_query() interpret their statement string argument as a single statement to be executed, and you process the result according to whether the statement produces a result set (a set of rows, as for SELECT) or an affected-rows count (as for INSERT, UPDATE, and so forth).

MySQL 4.1 also supports the execution of a string containing multiple statements separated by semicolon (“;”) characters. This capability is enabled by special options that are specified either when you connect to the server with mysql_real_connect() or after connecting by calling` mysql_set_server_option().

Executing a multiple-statement string can produce multiple result sets or row-count indicators. Processing these results involves a different approach than for the single-statement case: After handling the result from the first statement, it is necessary to check whether more results exist and process them in turn if so. To support multiple-result processing, the C API includes the mysql_more_results() and mysql_next_result() functions. These functions are used at the end of a loop that iterates as long as more results are available. Failure to process the result this way may result in a dropped connection to the server.

The multiple statement and result capabilities can be used only with mysql_query() or mysql_real_query(). They cannot be used with the prepared statement interface. Prepared statement handles are defined to work only with strings that contain a single statement. See Section 17.2.4, “C API Prepared Statements”.

To enable multiple-statement execution and result processing, the following options may be used:

  • The mysql_real_connect() function has a flags argument for which two option values are relevent:

    • CLIENT_MULTI_RESULTS enables the client program to process multiple results.

    • CLIENT_MULTI_STATEMENTS enables mysql_query() and mysql_real_query() to execute statement strings containing multiple statements separated by semicolons. This option also enables CLIENT_MULTI_RESULTS implicitly, so a flags argument of CLIENT_MULTI_STATEMENTS to mysql_real_connect() is equivalent to an argument of CLIENT_MULTI_STATEMENTS | CLIENT_MULTI_RESULTS. That is, CLIENT_MULTI_STATEMENTS is sufficient to enable multiple-statement execution and all multiple-result processing.

  • After the connection to the server has been established, you can use the mysql_set_server_option() function to enable or disable multiple-statement execution by passing it an argument of MYSQL_OPTION_MULTI_STATEMENTS_ON or MYSQL_OPTION_MULTI_STATEMENTS_OFF.

The following procedure outlines a suggested strategy for handling multiple statements:

  1. Pass CLIENT_MULTI_STATEMENTS to mysql_real_connect(), to fully enable multiple-statement execution and multiple-result processing.

  2. After calling mysql_query() or mysql_real_query() and verifying that it succeeds, enter a loop within which you process statement results.

  3. For each iteration of the loop, handle the current statement result, retrieving either a result set or an affected-rows count. If an error occurs, exit the loop.

  4. At the end of the loop, call mysql_next_result() to check whether another result exists and initiate retrieval for it if so. If no more results are available, exit the loop.

One possible implementation of the preceding strategy is shown following. The final part of the loop can be reduced to a simple test of whether mysql_next_result() returns non-zero. The code as written distinguishes between no more results and an error, which allows a message to be printed for the latter occurrence.

/* connect to server with the CLIENT_MULTI_STATEMENTS option */
if (mysql_real_connect (mysql, host_name, user_name, password,
    db_name, port_num, socket_name, CLIENT_MULTI_STATEMENTS) == NULL)
{
  printf("mysql_real_connect() failed\n");
  mysql_close(mysql);
  exit(1);
}

/* execute multiple statements */
status = mysql_query(mysql,
                     "DROP TABLE IF EXISTS test_table;\
                      CREATE TABLE test_table(id INT);\
                      INSERT INTO test_table VALUES(10);\
                      UPDATE test_table SET id=20 WHERE id=10;\
                      SELECT * FROM test_table;\
                      DROP TABLE test_table");
if (status)
{
  printf("Could not execute statement(s)");
  mysql_close(mysql);
  exit(0);
}

/* process each statement result */
do {
  /* did current statement return data? */
  result = mysql_store_result(mysql);
  if (result)
  {
    /* yes; process rows and free the result set */
    process_result_set(mysql, result);
    mysql_free_result(result);
  }
  else          /* no result set or error */
  {
    if (mysql_field_count(mysql) == 0)
    {
      printf("%lld rows affected\n",
            mysql_affected_rows(mysql));
    }
    else  /* some error occurred */
    {
      printf("Could not retrieve result set\n");
      break;
    }
  }
  /* more results? -1 = no, >0 = error, 0 = yes (keep looping) */
  if ((status = mysql_next_result(mysql)) > 0)
    printf("Could not execute statement\n");
} while (status == 0);

mysql_close(mysql);

17.2.10. C API Handling of Date and Time Values

The binary (prepared statement) protocol available in MySQL 4.1 and above allows you to send and receive date and time values (DATE, TIME, DATETIME, and TIMESTAMP), using the MYSQL_TIME structure. The members of this structure are described in Section 17.2.5, “C API Prepared Statement Data types”.

To send temporal data values, create a prepared statement using mysql_stmt_prepare(). Then, before calling mysql_stmt_execute() to execute the statement, use the following procedure to set up each temporal parameter:

  1. In the MYSQL_BIND structure associated with the data value, set the buffer_type member to the type that indicates what kind of temporal value you're sending. For DATE, TIME, DATETIME, or TIMESTAMP values, set buffer_type to MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, respectively.

  2. Set the buffer member of the MYSQL_BIND structure to the address of the MYSQL_TIME structure in which you pass the temporal value.

  3. Fill in the members of the MYSQL_TIME structure that are appropriate for the type of temporal value to be passed.

Use mysql_stmt_bind_param() to bind the parameter data to the statement. Then you can call mysql_stmt_execute().

To retrieve temporal values, the procedure is similar, except that you set the buffer_type member to the type of value you expect to receive, and the buffer member to the address of a MYSQL_TIME structure into which the returned value should be placed. Use mysql_stmt_bind_result() to bind the buffers to the statement after calling mysql_stmt_execute() and before fetching the results.

Here is a simple example that inserts DATE, TIME, and TIMESTAMP data. The mysql variable is assumed to be a valid connection handle.

  MYSQL_TIME  ts;
  MYSQL_BIND  bind[3];
  MYSQL_STMT  *stmt;

  strmov(query, "INSERT INTO test_table(date_field, time_field, \
                               timestamp_field) VALUES(?,?,?");

  stmt = mysql_stmt_init(mysql);
  if (!stmt)
  {
    fprintf(stderr, " mysql_stmt_init(), out of memory\n");
    exit(0);
  }
  if (mysql_stmt_prepare(mysql, query, strlen(query)))
  {
    fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  }

  /* set up input buffers for all 3 parameters */
  bind[0].buffer_type= MYSQL_TYPE_DATE;
  bind[0].buffer= (char *)&ts;
  bind[0].is_null= 0;
  bind[0].length= 0;
  ...
  bind[1]= bind[2]= bind[0];
  ...

  mysql_stmt_bind_param(stmt, bind);

  /* supply the data to be sent in the ts structure */
  ts.year= 2002;
  ts.month= 02;
  ts.day= 03;

  ts.hour= 10;
  ts.minute= 45;
  ts.second= 20;

  mysql_stmt_execute(stmt);
  ..

17.2.11. C API Threaded Function Descriptions

You need to use the following functions when you want to create a threaded client. See Section 17.2.16, “How to Make a Threaded Client”.

17.2.11.1. my_init()

void my_init(void)

Description

my_init() initializes some global variables that MySQL needs. If you are using a thread-safe client library, it also calls mysql_thread_init() for this thread.

It is necessary for my_init() to be called early in the initialization phase of a program's use of the MySQL library. However, my_init() is automatically called by mysql_init(), mysql_library_init(), mysql_server_init(), and mysql_connect(). If you ensure that your program invokes one of those functions before any other MySQL calls, there is no need to invoke my_init() explicitly.

To access my_init(), your program must include the my_sys.h header file:

#include "my_sys.h"

Return Values

None.

17.2.11.2. mysql_thread_end()

void mysql_thread_end(void)

Description

This function needs to be called before calling pthread_exit() to free memory allocated by mysql_thread_init().

mysql_thread_end() is not invoked automatically by the client library. It must be called explicitly to avoid a memory leak.

Return Values

None.

my_bool mysql_thread_init(void)

Description

This function must be called early within each created thread to initialize thread-specific variables. However, you may not necessarily need to invoke it explicitly: mysql_thread_init() is automatically called by my_init(), which itself is automatically called by mysql_init(), mysql_library_init(), mysql_server_init(), and mysql_connect(). If you invoke any of those functions, mysql_thread_init() will be called for you.

Return Values

Zero if successful. Non-zero if an error occurred.

unsigned int mysql_thread_safe(void)

Description

This function indicates whether the client library is compiled as thread-safe.

Return Values

1 if the client library is thread-safe, 0 otherwise.

17.2.12. C API Embedded Server Function Descriptions

MySQL applications can be written to use an embedded server. See Section 17.1, “libmysqld, the Embedded MySQL Server Library”. To write such an application, you must link it against the libmysqld library by using the -lmysqld flag rather than linking it against the libmysqlclient client library by using the -lmysqlclient flag. However, the calls to initialize and finalize the library are the same whether you write a client application or one that uses the embedded server: Call mysql_library_init() to initialize the library and mysql_library_end() when you are done with it. See Section 17.2.2, “C API Function Overview”.

mysql_library_init() and mysql_library_end() are available as of MySQL 4.1.10. For earlier versions of MySQL 4.1, call mysql_server_init() and mysql_server_end() instead, which are equivalent. mysql_library_init() and mysql_library_end() actually are #define symbols that make them equivalent to mysql_server_init() and mysql_server_end(), but the names more clearly indicate that they should be called when beginning and ending use of a MySQL C API library no matter whether the application uses libmysqlclient or libmysqld.

int mysql_server_init(int argc, char **argv, char **groups)

Description

This function initializes the MySQL library, which must be done before you call any other MySQL function.

As of MySQL 4.1.10, mysql_server_init() is deprecated and you should call mysql_library_init() instead. See Section 17.2.3.38, “mysql_library_init().

Return Values

Zero if successful. Non-zero if an error occurred.

17.2.12.2. mysql_server_end()

void mysql_server_end(void)

Description

This function finalizes the MySQL library. You should call it when you are done using the library.

As of MySQL 4.1.10, mysql_server_end() is deprecated and you should call mysql_library_end() instead. See Section 17.2.3.37, “mysql_library_end().

Return Values

None.

17.2.13. Controlling Automatic Reconnect Behavior

The MySQL client library can perform an automatic reconnect to the server if it finds that the connection is down when you attempt to send a statement to the server to be executed. In this case, the library tries once to reconnect to the server and send the statement again.

Some client programs might provide the capability of controlling automatic reconnection. For example, mysql reconnects by default, but the --skip-reconnect option can be used to suppress this behavior.

Automatic reconnection can be convenient because you need not implement your own reconnect code, but if a reconnection does occur, several aspects of the connection state are reset and your application will not know about it. The connection-related state is affected as follows:

  • Any active transactions are rolled back and autocommit mode is reset.

  • All table locks are released.

  • All TEMPORARY tables are closed (and dropped).

  • Session variables are reinitialized to the values of the corresponding variables. This also affects variables that are set implicitly by statements such as SET NAMES.

  • User variable settings are lost.

  • Prepared statements are released.

  • HANDLER variables are closed.

  • The value of LAST_INSERT_ID() is reset to 0.

  • Locks acquired with GET_LOCK() are released.

17.2.14. Common Questions and Problems When Using the C API

MySQL Enterprise Subscribers to MySQL Enterprise will find articles about the C API in the MySQL Knowledge Base. Access to the Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

17.2.14.1. Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success

It is possible for mysql_store_result() to return NULL following a successful call to mysql_query(). When this happens, it means one of the following conditions occurred:

  • There was a malloc() failure (for example, if the result set was too large).

  • The data couldn't be read (an error occurred on the connection).

  • The query returned no data (for example, it was an INSERT, UPDATE, or DELETE).

You can always check whether the statement should have produced a non-empty result by calling mysql_field_count(). If mysql_field_count() returns zero, the result is empty and the last query was a statement that does not return values (for example, an INSERT or a DELETE). If mysql_field_count() returns a non-zero value, the statement should have produced a non-empty result. See the description of the mysql_field_count() function for an example.

You can test for an error by calling mysql_error() or mysql_errno().

17.2.14.2. What Results You Can Get from a Query

In addition to the result set returned by a query, you can also get the following information:

17.2.14.3. How to Get the Unique ID for the Last Inserted Row

If you insert a record into a table that contains an AUTO_INCREMENT column, you can obtain the value stored into that column by calling the mysql_insert_id() function.

You can check from your C applications whether a value was stored in an AUTO_INCREMENT column by executing the following code (which assumes that you've checked that the statement succeeded). It determines whether the query was an INSERT with an AUTO_INCREMENT index:

if ((result = mysql_store_result(&mysql)) == 0 &&
    mysql_field_count(&mysql) == 0 &&
    mysql_insert_id(&mysql) != 0)
{
    used_id = mysql_insert_id(&mysql);
}

When a new AUTO_INCREMENT value has been generated, you can also obtain it by executing a SELECT LAST_INSERT_ID() statement with mysql_query() and retrieving the value from the result set returned by the statement.

For LAST_INSERT_ID(), the most recently generated ID is maintained in the server on a per-connection basis. It is not changed by another client. It is not even changed if you update another AUTO_INCREMENT column with a non-magic value (that is, a value that is not NULL and not 0). Using LAST_INSERT_ID() and AUTO_INCREMENT columns simultaneously from multiple clients is perfectly valid. Each client will receive the last inserted ID for the last statement that client executed.

If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:

INSERT INTO foo (auto,text)
    VALUES(NULL,'text');         # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
    VALUES(LAST_INSERT_ID(),'text');  # use ID in second table

Note that mysql_insert_id() returns the value stored into an AUTO_INCREMENT column, whether that value is automatically generated by storing NULL or 0 or was specified as an explicit value. LAST_INSERT_ID() returns only automatically generated AUTO_INCREMENT values. If you store an explicit value other than NULL or 0, it does not affect the value returned by LAST_INSERT_ID().

For more information on obtaining the last ID in an AUTO_INCREMENT column:

17.2.14.4. Problems Linking with the C API

When linking with the C API, the following errors may occur on some systems:

gcc -g -o client test.o -L/usr/local/lib/mysql \
                        -lmysqlclient -lsocket -lnsl

Undefined        first referenced
 symbol          in file
floor            /usr/local/lib/mysql/libmysqlclient.a(password.o)
ld: fatal: Symbol referencing errors. No output written to client

If this happens on your system, you must include the math library by adding -lm to the end of the compile/link line.

17.2.15. Building Client Programs

If you compile MySQL clients that you've written yourself or that you obtain from a third-party, they must be linked using the -lmysqlclient -lz options in the link command. You may also need to specify a -L option to tell the linker where to find the library. For example, if the library is installed in /usr/local/mysql/lib, use -L/usr/local/mysql/lib -lmysqlclient -lz in the link command.

For clients that use MySQL header files, you may need to specify an -I option when you compile them (for example, -I/usr/local/mysql/include), so that the compiler can find the header files.

To make it simpler to compile MySQL programs on Unix, we have provided the mysql_config script for you. See Section 4.7.2, “mysql_config — Get Compile Options for Compiling Clients”.

You can use it to compile a MySQL client as follows:

CFG=/usr/local/mysql/bin/mysql_config
sh -c "gcc -o progname `$CFG --cflags` progname.c `$CFG --libs`"

The sh -c is needed to get the shell not to treat the output from mysql_config as one word.

MySQL Enterprise Subscribers to MySQL Enterprise will find an example client program in the Knowledge Base article, Sample C program using the embedded MySQL server library . Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.

17.2.16. How to Make a Threaded Client

The client library is almost thread-safe. The biggest problem is that the subroutines in net.c that read from sockets are not interrupt safe. This was done with the thought that you might want to have your own alarm that can break a long read to a server. If you install interrupt handlers for the SIGPIPE interrupt, the socket handling should be thread-safe.

Note

Beginning with version 4.0.6, MySQL blocks SIGPIPE on the first call to mysql_server_init(), mysql_init(), or mysql_connect(). This is done to avoid aborting the program when a connection terminates. If you want to use your own SIGPIPE handler, you should first call mysql_server_init() and then install your handler. As of MySQL 4.1.10, use mysql_library_init() instead of mysql_server_init().

Before MySQL 4.0, binary client libraries that we provided other than those for Windows were not normally compiled with the thread-safe option. Current binary distributions should have both a normal and a thread-safe client library.

To create a threaded client where you can interrupt the client from other threads and set timeouts when talking with the MySQL server, you should use the net_serv.o code that the server uses and the -lmysys, -lmystrings, and -ldbug libraries.

If you don't need interrupts or timeouts, you can just compile a thread-safe client library (mysqlclient_r) and use it. In this case, you don't have to worry about the net_serv.o object file or the other MySQL libraries.

When using a threaded client and you want to use timeouts and interrupts, you can make great use of the routines in the thr_alarm.c file. If you are using routines from the mysys library, the only thing you must remember is to call my_init() first! See Section 17.2.11, “C API Threaded Function Descriptions”.

In all cases, be sure to initialize the client library by calling mysql_library_init() before calling any other MySQL functions. When you are done with the library, call mysql_library_end().

mysql_real_connect() is not thread-safe by default. The following notes describe how to compile a thread-safe client library and use it in a thread-safe manner. (The notes below for mysql_real_connect() also apply to the older mysql_connect() routine as well, although mysql_connect() is deprecated and should no longer be used.)

To make mysql_real_connect() thread-safe, you must configure your MySQL distribution with this command:

shell> ./configure --enable-thread-safe-client

Then recompile the distribution to create a thread-safe client library, libmysqlclient_r. (Assuming that your operating system has a thread-safe gethostbyname_r() function.) This library is thread-safe per connection. You can let two threads share the same connection with the following caveats:

  • Two threads can't send a query to the MySQL server at the same time on the same connection. In particular, you have to ensure that between calls to mysql_query() and mysql_store_result(), no other thread is using the same connection.

  • Many threads can access different result sets that are retrieved with mysql_store_result().

  • If you use mysql_use_result(), you must ensure that no other thread is using the same connection until the result set is closed. However, it really is best for threaded clients that share the same connection to use mysql_store_result().

  • If you want to use multiple threads on the same connection, you must have a mutex lock around your pair of mysql_query() and mysql_store_result() calls. Once mysql_store_result() is ready, the lock can be released and other threads may query the same connection.

  • If you use POSIX threads, you can use pthread_mutex_lock() and pthread_mutex_unlock() to establish and release a mutex lock.

  • mysql_ping() does not attempt a reconnection if the connection is down. It returns an error instead.

You need to know the following if a thread that is calling MySQL functions did not create the connection to the MySQL database:

When you call mysql_init(), MySQL creates a thread-specific variable for the thread that is used by the debug library (among other things). If you call a MySQL function before the thread has called mysql_init(), the thread does not have the necessary thread-specific variables in place and you are likely to end up with a core dump sooner or later. To get things to work smoothly you must do the following:

  1. Call mysql_library_init() before any other MySQL functions. It is not thread-safe, so call it before threads are created, or protect the call with a mutex.

  2. Arrange for mysql_thread_init() to be called early in the thread handler before calling any MySQL function. If you call mysql_init(), they will call mysql_thread_init() for you.

  3. In the thread, call mysql_thread_end() before calling pthread_exit(). This frees the memory used by MySQL thread-specific variables.

The preceding notes regarding mysql_init() also apply to mysql_connect(), which calls mysql_init().

If “undefined symbol” errors occur when linking your client with libmysqlclient_r, in most cases this is because you haven't included the thread libraries on the link/compile command.

17.3. MySQL PHP API

PHP is a server-side, HTML-embedded scripting language that may be used to create dynamic Web pages. It is available for most operating systems and Web servers, and can access most common databases, including MySQL. PHP may be run as a separate program or compiled as a module for use with the Apache Web server.

PHP actually provides two different MySQL API extensions:

  • mysql: Available for PHP versions 4 and 5, this extension is intended for use with MySQL versions prior to MySQL 4.1. This extension does not support the improved authentication protocol used in MySQL 4.1, nor does it support prepared statements or multiple statements. If you wish to use this extension with MySQL 4.1, you will likely want to configure the MySQL server to use the --old-passwords option (see Section A.1.2.4, “Client does not support authentication protocol). This extension is documented on the PHP Web site at http://php.net/mysql.

  • mysqli - Stands for “MySQL, Improved”; this extension is available only in PHP 5. It is intended for use with MySQL 4.1.1 and later. This extension fully supports the authentication protocol used in MySQL 5.0, as well as the Prepared Statements and Multiple Statements APIs. In addition, this extension provides an advanced, object-oriented programming interface. You can read the documentation for the mysqli extension at http://php.net/mysqli. A helpful article can be found at http://www.zend.com/php5/articles/php5-mysqli.php.

If you're experiencing problems with enabling both the mysql and the mysqli extension when building PHP on Linux yourself, see Section 17.3.2, “Enabling Both mysql and mysqli in PHP”.

The PHP distribution and documentation are available from the PHP Web site. MySQL provides the mysql and mysqli extensions for the Windows operating system on http://dev.mysql.com/downloads/connector/php/. You can find information why you should preferably use the extensions provided by MySQL on that page.

MySQL Enterprise MySQL Enterprise subscribers will find more information about MySQL and PHP in the Knowledge Base articles found at PHP. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/knowledgebase.html.

17.3.1. Common Problems with MySQL and PHP

  • Error: Maximum Execution Time Exceeded: This is a PHP limit; go into the php.ini file and set the maximum execution time up from 30 seconds to something higher, as needed. It is also not a bad idea to double the RAM allowed per script to 16MB instead of 8MB.

  • Fatal error: Call to unsupported or undefined function mysql_connect() in ...: This means that your PHP version isn't compiled with MySQL support. You can either compile a dynamic MySQL module and load it into PHP or recompile PHP with built-in MySQL support. This process is described in detail in the PHP manual.

  • Error: Undefined reference to 'uncompress': This means that the client library is compiled with support for a compressed client/server protocol. The fix is to add -lz last when linking with -lmysqlclient.

  • Error: Client does not support authentication protocol: This is most often encountered when trying to use the older mysql extension with MySQL 4.1.1 and later. Possible solutions are: downgrade to MySQL 4.0; switch to PHP 5 and the newer mysqli extension; or configure the MySQL server with --old-passwords. (See Section A.1.2.4, “Client does not support authentication protocol, for more information.)

Those with PHP4 legacy code can make use of a compatibility layer for the old and new MySQL libraries, such as this one: http://www.coggeshall.org/oss/mysql2i.

17.3.2. Enabling Both mysql and mysqli in PHP

If you're experiencing problems with enabling both the mysql and the mysqli extension when building PHP on Linux yourself, you should try the following procedure.

  1. Configure PHP like this:

    ./configure --with-mysqli=/usr/bin/mysql_config --with-mysql=/usr  
    

  2. Edit the Makefile and search for a line that starts with EXTRA_LIBS. It might look like this (all on one line):

    EXTRA_LIBS = -lcrypt -lcrypt -lmysqlclient -lz -lresolv -lm -ldl -lnsl
    -lxml2 -lz -lm -lxml2 -lz -lm -lmysqlclient -lz -lcrypt -lnsl -lm
    -lxml2 -lz -lm -lcrypt -lxml2 -lz -lm -lcrypt
    

    Remove all duplicates, so that the line looks like this (all on one line):

    EXTRA_LIBS = -lcrypt -lcrypt -lmysqlclient -lz -lresolv -lm -ldl -lnsl
    -lxml2
    

  3. Build and install PHP:

    make
    make install
    

MySQL Enterprise MySQL Enterprise subscribers will find more information about the mysqli extension in the Knowledge Base articles found at mysqli. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.

17.4. MySQL Perl API

The Perl DBI module provides a generic interface for database access. You can write a DBI script that works with many different database engines without change. To use DBI, you must install the DBI module, as well as a DataBase Driver (DBD) module for each type of server you want to access. For MySQL, this driver is the DBD::mysql module.

Perl DBI is the recommended Perl interface. It replaces an older interface called mysqlperl, which should be considered obsolete.

Installation instructions for Perl DBI support are given in Section 2.15, “Perl Installation Notes”.

DBI information is available at the command line, online, or in printed form:

  • Once you have the DBI and DBD::mysql modules installed, you can get information about them at the command line with the perldoc command:

    shell> perldoc DBI
    shell> perldoc DBI::FAQ
    shell> perldoc DBD::mysql
    

    You can also use pod2man, pod2html, and so forth to translate this information into other formats.

  • For online information about Perl DBI, visit the DBI Web site, http://dbi.perl.org/. That site hosts a general DBI mailing list. MySQL AB hosts a list specifically about DBD::mysql; see Section 1.6.1, “MySQL Mailing Lists”.

  • For printed information, the official DBI book is Programming the Perl DBI (Alligator Descartes and Tim Bunce, O'Reilly & Associates, 2000). Information about the book is available at the DBI Web site, http://dbi.perl.org/.

    For information that focuses specifically on using DBI with MySQL, see MySQL and Perl for the Web (Paul DuBois, New Riders, 2001). This book's Web site is http://www.kitebird.com/mysql-perl/.

17.5. MySQL C++ API

MySQL++ is a MySQL API for C++. Warren Young has taken over this project. More information can be found at http://tangentsoft.net/mysql++/doc.

MySQL Enterprise MySQL Enterprise subscribers will find more information about using C++ with the MySQL API in the MySQL Knowledge Base. articles found at C++. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.

17.6. MySQL Python API

MySQLdb provides MySQL support for Python, compliant with the Python DB API version 2.0. It can be found at http://sourceforge.net/projects/mysql-python/.

MySQL Enterprise MySQL Enterprise subscribers will find more information about using Python with the MySQL API in the MySQL Knowledge Base articles found at Python. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.

17.7. MySQL Tcl API

MySQLtcl is a simple API for accessing a MySQL database server from the Tcl programming language. It can be found at http://www.xdobry.de/mysqltcl/.

17.8. MySQL Eiffel Wrapper

Eiffel MySQL is an interface to the MySQL database server using the Eiffel programming language, written by Michael Ravits. It can be found at http://efsa.sourceforge.net/archive/ravits/mysql.htm.