#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char **argv) 
{
  pid_t pid;

  /* Create a shared memory segment */
  int segment_id;
  segment_id = shmget(IPC_PRIVATE, 10*sizeof(char), IPC_R | IPC_W);
  if (segment_id == -1) {
    fprintf(stderr,"Can't create a new shared memory segment\n");
    perror("shmget()");
    exit(1);
  }
  fprintf(stdout,"Created a shared memory segment with id %d\n",
                 segment_id);

  /* Create a child process */
  pid = fork();
  if (pid == -1) {
    fprintf(stderr,"Can't create a new process\n");
    perror("fork()");
    exit(1);
  }

  if (pid) { // parent

    fprintf(stdout,"Created a child\n");
    /* Attach the memory segment */
    char *shared_memory = (char *)shmat(segment_id, NULL, 0);
    if (!shared_memory) {
      fprintf(stderr,"Can't attach new memory segment\n");
      perror("shmat()");
      exit(1);
    }

    /* Writing to the shared memory segment */
    sprintf(shared_memory, "hello");
    fprintf(stdout,"Parent: wrote 'hello' in shared memory region\n");
  
    /* Waiting for my child to exit */
    fprintf(stdout,"Parent: waiting for child\n");
    if (waitpid(pid, NULL, 0) != pid) {
      fprintf(stderr,"Can't wait for child\n");
      perror("waitpid()");
      exit(1); 
    }

    /* Detaching the shared memory segment */
    if (shmdt(shared_memory) == -1) {
      fprintf(stderr,"Can't detach memory segment\n");
      perror("shmdt()");
      exit(1);
    }
    fprintf(stdout,"Parent: detached memory segment\n");

    /* Removing the shared memory segment */
    if (shmctl(segment_id, IPC_RMID, NULL)) {
      fprintf(stderr,"Can't remove memory segment\n");
      perror("shmctl()");
      exit(1);
    }
    fprintf(stdout,"Parent: removed memory segment\n");
   
  } else { // child

    /* Sleeping */
    sleep(2);

    /* Attaching the shared memory segment */
    char *shared_memory = (char *)shmat(segment_id, NULL, 0);
    if (!shared_memory) {
      fprintf(stderr,"Can't attach new memory segment\n");
      perror("shmat()");
      exit(1);
    }
    fprintf(stdout,"Child: attached memory segment\n");

    /* Reading the content of the shared memory */
    fprintf(stdout,"Child: read '%s' in shared memory region\n", 
               shared_memory);
    /* Detaching the shared memory segment */
    if (shmdt(shared_memory) == -1) {
      fprintf(stderr,"Can't detach memory segment\n");
      perror("shmdt()");
      exit(1);
    }
    fprintf(stdout,"Child: detached memory segment\n");

    fprintf(stdout,"Child: exiting\n");
    exit(0);
  }

  exit(0);
}