MySQL :: MySQL 8.4 C API Developer Guide :: 5.4.22 mysql_fetch_row() (original) (raw)

5.4.22 mysql_fetch_row()

MYSQL_ROW
mysql_fetch_row(MYSQL_RES *result)

Description

Note

mysql_fetch_row() is a synchronous function. Its asynchronous counterpart ismysql_fetch_row_nonblocking(), for use by applications that require asynchronous communication with the server. SeeChapter 7, C API Asynchronous Interface.

mysql_fetch_row() retrieves the next row of a result set:

• When used aftermysql_store_result() ormysql_store_result_nonblocking(),mysql_fetch_row() returnsNULL if there are no more rows to retrieve.
• When used aftermysql_use_result(),mysql_fetch_row() returnsNULL if there are no more rows to retrieve or an error occurred.

The number of values in the row is given bymysql_num_fields(result). Ifrow holds the return value from a call tomysql_fetch_row(), pointers to the values are accessed as row[0] torow[mysql_num_fields(result)-1].NULL values in the row are indicated byNULL 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 isNULL, the field is NULL; otherwise, the field is empty.

Return Values

A MYSQL_ROW structure for the next row, orNULL. The meaning of aNULL return depends on which function was called precedingmysql_fetch_row():

• When used aftermysql_store_result() ormysql_store_result_nonblocking(),mysql_fetch_row() returnsNULL if there are no more rows to retrieve.
• When used aftermysql_use_result(),mysql_fetch_row() returnsNULL if there are no more rows to retrieve or an error occurred. To determine whether an error occurred, check whethermysql_error() returns a nonempty string ormysql_errno() returns nonzero.

Errors

Errors are not reset between calls tomysql_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");
}