al_get_errno - Man Page

int al_get_errno(void)
GETTER(allegro_errno, 0)

Some Allegro functions will set an error number as well as returning an error code. Call this function to retrieve the last error number set for the calling thread.

al_fflush(3), al_fixdiv(3), al_fixmul(3), al_fixsub(3), al_fseek(3), al_ftell(3), al_ftofix(3), al_fungetc(3), al_get_current_directory(3), al_get_fs_entry_mode(3), al_make_directory(3), al_update_fs_entry(3).