27.7.6.48 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)
.
Returns the number of columns in a result set.
You can get the number of columns either from a pointer to a result set or to a connection handler. You would use the connection handler 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 nonempty result. This enables 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.
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.