This function is used to check current state of connection. Connection state is stored at *state, line and file of library, where the error was set, are stored at *file and *line. Any of these three is not stored if pointer is NULL.
yw_strerror(3) function can be used to translate returned value into human-readable string. yw_conn_state(3) may be more handy in regular situation, when you don't want to debug the library. yw_conn_state(conn) is equivalent to yw_conn_get_state(conn, NULL, NULL, NULL).