file auth_demo.c in sample code as following:
static void handle_open_worker(es_client_t *x, const es_message_t *msg) { static const char *ro_prefix = "/usr/local/bin/";
//ro_prefix_length will always equal 7,since sizeof(char*)=8
static const size_t ro_prefix_length = sizeof(ro_prefix) - 1;
...... }