20.4.35 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.

20.4.35.1 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() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether or not mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether or not the query was a SELECT (or SELECT-like) statement. The example shown below illustrates how this may be done.

NULL mysql_store_result().

20.4.35.2 Return values

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

20.4.35.3 Errors

None.

20.4.35.4 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:@: %sn", 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 if mysql_field_count(&mysql) is = 0. This will only happen if something went wrong.