// shmCreateAndWrite.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>

int main ()

{
  int segment_id;
  char bogus;
  char* shared_memory;
  struct shmid_ds shmbuffer;
  int segment_size;
  const int shared_segment_size = 0x6400;

  /* Allocate a shared memory segment.  */
  segment_id = shmget (IPC_PRIVATE, shared_segment_size, IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
  /* Attach the shared memory segment.  */
  printf("Shared memory segment ID is %d\n", segment_id);
  shared_memory = (char*) shmat (segment_id, 0, 0);
  printf ("shared memory attached at address %p\n", shared_memory);
  /* Determine the segment's size. */
  /*
  shmctl (segment_id, IPC_STAT, &shmbuffer);
  segment_size  =               shmbuffer.shm_segsz;
  printf ("segment size: %d\n", segment_size);
  */
  /* Write a string to the shared memory segment.  */
  sprintf (shared_memory, "Hello, world.");
  /* Detach the shared memory segment.  */
  shmdt (shared_memory);
  printf("Wrote Hello World to the segment\n");

}

// shmDeleteExisting.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>

int main ()

{
  int segment_id;

  printf("Enter the shared memory id: ");
  scanf("%d", &segment_id);

  /* Deallocate the segment.  */
  shmctl (segment_id, IPC_RMID, 0);

  return 0;

}

// shmReadExisting.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>

int main ()

{
  int segment_id;
  char bogus;
  char* shared_memory;
  struct shmid_ds shmbuffer;
  int segment_size;
  const int shared_segment_size = 0x6400;

  printf("Enter the shared memory id: ");
  scanf("%d", &segment_id);

  /* Reattach the shared memory segment, at a different address.  */
  shared_memory = (char*) shmat (segment_id, (void*) 0x5000000, 0);
  printf ("shared memory reattached at address %p\n", shared_memory);
  /* Print out the string from shared memory.  */
  printf ("The contents of the shared memory is:\n%s\n", shared_memory);
  /* Detach the shared memory segment.  */
  shmdt (shared_memory);

  return 0;

}

// shmWriteExisting.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <time.h>

int main ()

{
  int segment_id;
  char bogus;
  char* shared_memory;
  struct shmid_ds shmbuffer;
  int segment_size;
  const int shared_segment_size = 0x6400;

  time_t t;
  time(&t);

  printf("Enter the shared memory id: ");
  scanf("%d", &segment_id);

  /* Reattach the shared memory segment, at a different address.  */
  shared_memory = (char*) shmat (segment_id, (void*) 0x5000000, 0);
  printf ("shared memory reattached at address %p\n", shared_memory);

  /* Add to the segment */
  sprintf (shared_memory, "Modified the segment at %s", ctime(&t));

  /* Print out the string from shared memory.  */
  printf ("The contents of the shared memory is:\n%s", shared_memory);
  printf ("#################################################\n");

  return 0;

}