#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wimplicit-function-declaration"
#include <stdio.h>
#include <stdlib.h>

void prepare() { printf("preparing for fork...\n"); }

void parent() { printf("in parent after fork...\n"); }

void child() { printf("in child after fork...\n"); }

int main() {
  __register_atfork(prepare, parent, child);
  pid_t pid = fork();
  if (pid == 0) {
    // in child process
    printf("I am the child!\n");
  } else {
    // in parent process
    printf("I am the parent!\n");
  }
  return 0;
}

#pragma GCC diagnostic pop