int create_semaphor(union semun ctl, char letter){
    key_t key;                          //klucze semaforów
    int semid;

    if ((key = ftok(".", letter)) == -1)
        errx(1, "Blad tworzenia klucza!");

    if ((semid = semget(key, 1, IPC_CREAT | 0600)) == -1)
        errx(2, "Blad tworzenia semafora!");

    ctl.val = 1;
    if (semctl(semid, 0, SETVAL, ctl) == -1)
        errx(3, "Blad ustawiania semafora!");

    return semid;
}




    semid0 = create_semaphor(ctl, 'a');
    semid1 = create_semaphor(ctl, 'b');
    semid2 = create_semaphor(ctl, 'g');