25.2.3.46. mysql_num_fields()
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 25.2.13.1, “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.
