unsigned long long mysql_stmt_num_rows(MYSQL_STMT * stmt);
stmt- a statement handle, which was previously allocated by mysql_stmt_init().
Returns the number of rows in the result set. The use of mysql_stmt_num_rows() depends on whether or not you used mysql_stmt_store_result() to buffer the entire result set in the statement handle.
If you use mysql_stmt_store_result(), mysql_stmt_num_rows() may be called immediately.