22.2. MySQL C API

my_bool mysql_more_results(MYSQL *mysql)

Description

Returns true if more results exist from the currently executed query, and the application must call mysql_next_result() to fetch the results.

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 22.2.9, “C API Handling of Multiple Statement Execution”, and Section 22.2.3.45, “mysql_next_result()”.

Errors

None.

int mysql_next_result(MYSQL *mysql)

Description

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

You must call mysql_free_result() for the preceding query if it 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 query. 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.

If your program executes stored procedures with the CALL SQL statement, you must set the CLIENT_MULTI_RESULTS flag, either explicitly, or implicitly by setting CLIENT_MULTI_STATEMENTS when you call mysql_real_connect(). This is because each CALL returns a result to indicate the call status, in addition to any results sets that might be returned by statements executed within the procedure. In addition, because CALL can return multiple results, you should process those results using a loop that calls mysql_next_result() to determine whether there are more results.

For an example that shows how to use mysql_next_result(), see Section 22.2.9, “C API Handling of Multiple Statement Execution”.

Return Values

Errors

unsigned int mysql_num_fields(MYSQL_RES *result)

To pass a MYSQL* argument instead, use unsigned int mysql_field_count(MYSQL *mysql).

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 22.2.13.1, “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) is = 0. This happens only if something went wrong.

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.

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, then arg should point to the value of the integer.

Possible option values:

Note that 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:

Note that timeout has been replaced by connect-timeout, but timeout is still supported in MySQL 5.0.25 for backward compatibility.

For more information about option files, see Section 4.3.2, “Using Option Files”.

Return Values

Zero for success. Non-zero if you used 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 the client to use the compressed client/server protocol and read the additional options from the odbc section in the my.cnf file.

int mysql_ping(MYSQL *mysql)

Description

Checks whether the connection to the server is working. If the connection has gone down, an automatic reconnection is attempted.

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

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

Description

Executes the SQL query pointed to by the null-terminated string query. 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 22.2.9, “C API Handling of Multiple Statement Execution”.

mysql_query() cannot be used for queries that contain binary data; you should use mysql_real_query() instead. (Binary data may contain the ‘\0’ character, which mysql_query() interprets as the end of the query string.)

If you want to know whether the query should return a result set, you can use mysql_field_count() to check for this. See Section 22.2.3.22, “mysql_field_count()”.

Return Values

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

Errors

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:

If your program executes stored procedures with the CALL SQL statement, you must set the CLIENT_MULTI_RESULTS flag, either explicitly, or implicitly by setting CLIENT_MULTI_STATEMENTS when you call mysql_real_connect(). This is because each CALL returns a result to indicate the call status, in addition to any results sets that might be returned by statements executed within the procedure.

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 22.2.9, “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:

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

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 in versions of the API older than 5.0.3, or 0 in newer versions. 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. As of MySQL 5.0.13, you can use the MYSQL_OPT_RECONNECT option to mysql_options() to control reconnection behavior.

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 9.1.1, “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 9.1, “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.

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

Description

Executes the SQL query pointed to by query, 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 22.2.9, “C API Handling of Multiple Statement Execution”.

You must use mysql_real_query() rather than mysql_query() for queries that contain binary data, because binary data may contain the ‘\0’ character. In addition, mysql_real_query() is faster than mysql_query() because it does not call strlen() on the query string.

If you want to know whether the query should return a result set, you can use mysql_field_count() to check for this. See Section 22.2.3.22, “mysql_field_count()”.

Return Values

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

Errors

int mysql_refresh(MYSQL *mysql, unsigned int options)

Description

This functions 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.

Return Values

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

Errors

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

my_bool mysql_rollback(MYSQL *mysql)

Description

Rolls back the current transaction.

As of MySQL 5.0.3, the action of this function is subject to the value of the completion_type system variable. In particular, if the value of completion_type is 2, the server performs a release after terminating a transaction and closes the client connection. The client program should call mysql_close() to close the connection from the client side.

Return Values

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

Errors

None.

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.

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.

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

int mysql_set_character_set(MYSQL *mysql, 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 5.0.7.

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) datafile 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 datafile, 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:

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 22.2.9, “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. If you are using the CALL SQL statement in your programs, multiple-result support must be enabled; this means that MYSQL_OPTION_MULTI_STATEMENTS_ON by itself is insufficient to allow the use of CALL.

Return Values

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

Errors

int mysql_shutdown(MYSQL *mysql, enum 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 5.0.1. MySQL 5.0 servers support 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 5.2.6, “The MySQL Server Shutdown Process”.

Return Values

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

Errors

const char *mysql_sqlstate(MYSQL *mysql)

Description

Returns a null-terminated string containing the SQLSTATE error code for the last error. 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 B, Error Codes and Messages.

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

Return Values

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

See Also

See Section 22.2.3.14, “mysql_errno()”, Section 22.2.3.15, “mysql_error()”, and Section 22.2.7.26, “mysql_stmt_sqlstate()”.

int 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:

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.

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

MYSQL_RES *mysql_store_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, CHECK TABLE, and so forth).

You don't have to call mysql_store_result() or mysql_use_result() for other queries, 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 if the query didn't have a result set by checking if mysql_store_result() returns 0 (more about this later on).

If you want to know whether the query should return a result set, you can use mysql_field_count() to check for this. See Section 22.2.3.22, “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 query didn't return a result set (if the query was, for example, 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 if mysql_error() returns a non-empty string, if mysql_errno() returns non-zero, or if 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.)

Once you have called mysql_store_result() and got a result back that isn't a null pointer, you may 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.

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

See Section 22.2.13.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

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

Errors

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

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.

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.

unsigned int mysql_warning_count(MYSQL *mysql)

Description

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

Return Values

The warning count.

Errors

None.