MySQL 5.7 C API Developer Guide
void mysql_free_result(MYSQL_RES *result)
mysql_free_result() frees the
memory allocated for a result set by
mysql_store_result(),
mysql_use_result(),
mysql_list_dbs(), and so
forth. When you are done with a result set, you must free the
memory it uses by calling
mysql_free_result().
Do not attempt to access a result set after freeing it.