Opaque type example

living_being.c

#include "living_being.h"

struct living_being {
    int meaning;
};

#include <stdlib.h>

void give_birth(living_being **toilet) {
    *toilet = malloc(sizeof **toilet);
}

void install_meaning_of_life(living_being **subject) {
    (*subject)->meaning = 42;
}

void kill_tragically(living_being **organ_donor) {
    free(*organ_donor);
    *organ_donor = NULL;
}

living_being.h

#ifndef INCLUDED_LIVING_BEING
#define INCLUDED_LIVING_BEING

struct living_being;
typedef struct living_being living_being;

void give_birth(struct living_being **);
void install_meaning_of_life(struct living_being **);
void kill_tragically(struct living_being **);
#endif

main.c

#include <stdlib.h>
#include "living_being.h"

int main(void) {
    living_being *Chris_Pirillo = NULL;
    give_birth(&Chris_Pirillo);
    install_meaning_of_life(&Chris_Pirillo);
    kill_tragically(&Chris_Pirillo);
}