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

typedef struct test
{
  char a[256];
  char *b;
  char c[256];
} test;


#define SHM_CREATE 1
#define SHM_LOAD 0
#define SHM_FILE "/var/test.shm"
#define SHM_SIZE 8000

char *
init_shm (const int flag, char *pathname, const unsigned long size, int shmid)
{
  char *ret = NULL;
  int shm_id = 0;
  key_t key = ftok (pathname, 'R');
  if (SHM_CREATE == flag)    // 新建 
    {
      shm_id = shmget (key, size, IPC_CREAT | IPC_EXCL | 0600);
      if (-1 == shm_id)
    {
      shm_id = shmget (key, size, 0);
      if (-1 == shm_id)
        {
          perror ("init_shm shmget create");
          return NULL;
        }
    }
      printf("shm_id = %d\n", shm_id);
      if ((ret = shmat (shm_id, (char *) 0xb7f17000, 0)) == (void *)-1) {
    perror("shmat");
    exit(1);
      }
      memset (ret, 0, size);
    }
  else
    {/*
      shm_id = shmget (key, size, 0);
      if (shm_id == -1)
    {
      perror ("init_shm shmget load");
      return NULL;
    }
     */
      ret = shmat (shmid, (char *)0xb7f17000, 0);
    }
  return ret;
}

int
main (int argc, char **argv)
{
  int shmid;
  char *arg = argv[1];

  if (argc != 3) {
    printf("Usage: %s cmd shmid\n", argv[0]);
    exit(1);
  }

  if (*arg == 'c')
    {
      system ("touch " SHM_FILE);    // create shm file 
      printf("SHM_FILE' size = %d\n", SHM_SIZE);
      test *t = (struct test *) init_shm (SHM_CREATE, SHM_FILE, SHM_SIZE, shmid);
      t->b = t->c;

      if (t)
    {
      printf("t->a size = %d\n", sizeof(t->a));
      //t->b =(char *) t + sizeof(t->a);
      printf ("addr = 0x%08x/0x%08x\n", (unsigned int)t->b, (unsigned int)t);
      strcpy (t->a, "AAAA");
      strcpy (t->b, "111");
      printf ("a=%s,b=%s\n", t->a, t->b);
    }
    }
  else if (*arg == 'l')
    {
      shmid = atoi(argv[2]);
      test *t = (struct test *) init_shm (SHM_LOAD, SHM_FILE, SHM_SIZE, shmid);
      printf ("addr = 0x%08x/0x%08x\n",(unsigned int)t->b, (unsigned int)t);
      //t->b = (char *)t + sizeof(struct test); // 重新定位b的位置 
      if (t)
    {
      printf ("a=%s,b=%s\n", t->a, t->b);
    }
    }
  return 0;
}