8.24

/* $begin waitpid1 */
#include "csapp.h"
#define N 2
#define LEN 100

int main() {
  int status, i;
  pid_t pid;

  /* Parent creates N children */
  for (i = 0; i < N; i++)
    if ((pid = Fork()) == 0) {
      /* access address 0, cause fault */
      char* cptr = NULL;
      *cptr = 'd';
    }

  /* Parent reaps N children in no particular order */
  while ((pid = waitpid(-1, &status, 0)) > 0) {
    if (WIFEXITED(status))
      printf("child %d terminated normally with exit status=%d\n",
          pid, WEXITSTATUS(status));
    else if (WIFSIGNALED(status)) {
      /* print signal that cause process exit */
      char buf[LEN];
      sprintf(buf, "child %d terminated by signal %d", pid, WTERMSIG(status));
      psignal(WTERMSIG(status), buf);
    }
    else
      printf("child %d terminated abnormally\n", pid);
  }

  /* The only normal termination is if there are no more children */
  if (errno != ECHILD)
    unix_error("waitpid error");

  exit(0);
}
/* $end waitpid1 */