Allegro 5 api
#include <allegro5/allegro.h> int al_ustr_find_cset(const ALLEGRO_USTR *us, int start_pos, const ALLEGRO_USTR *reject)
This function finds the first code point in us, beginning from byte offset start_pos, that does not match any code point in reject. In other words it finds a code point in the complementary set of reject. Returns the byte position of that code point, if any. Otherwise returns -1.
al_ustr_find_cset_cstr(3alleg5), al_ustr_find_set(3alleg5)