共享内存问题 shmat返回值与ipcs -m 值不一致

[玉生香]

#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/shm.h>
#include <errno.h>
#include <stdio.h>
#include <strings.h>

#define err_abort(code,text) do { \
    fprintf (stderr, "%s at \"%s\":%d: %s\n", \
        text, __FILE__, __LINE__, strerror (code)); \
    abort (); \
    } while (0)
#define errno_abort(text) do { \
    fprintf (stderr, "%s at \"%s\":%d: %s\n", \
        text, __FILE__, __LINE__, strerror (errno)); \
    abort (); \
    } while (0)


key_t shm_key = -1;
int shm_id;



struct INFORMATION
{
   int  Inf_No;//编号
   int  Inf_Information;//信息
   bool Inf_IsFill;
};

INFORMATION* pShmHead = NULL;
INFORMATION* pShmTail = NULL;


/*共享内存操作*/
bool GetShm(key_t & shm_key,const int &flag)
{
   if( (shm_id = shmget(shm_key,sizeof(INFORMATION)*5,IPC_CREAT|IPC_EXCL|flag)) == -1)
   {
      if(errno == EEXIST)
      {
         if(shmget(shm_key,sizeof(INFORMATION)*5,flag)>-1)
         {
            return true;
         }
      }
      err_abort(errno,"Create share memory");   
   }
   return true;
}

bool AttacheShm(key_t& shm_id,const void *shmaddr,const int &flag)
{
   if((pShmHead = (INFORMATION*)shmat(shm_id,shmaddr,flag)) == NULL)
       err_abort(errno,"Attache share memory");
   return true;
}


bool DeacheShm(const void *shmaddr)
{
   if(shmdt(shmaddr)==-1)
       err_abort(errno,"DeacheShm share memory");
   return true;
}


bool RemoveShm(key_t& shm_key)
{
   if(shmctl(shm_key, IPC_RMID, NULL) == -1)
      err_abort(errno,"RemoveShm share memory");
   return true;
}


/*
void * routine(void* arg)
{
   INFORMATION* p ;
      for(p = pShmHead;p!=pShmTail;p++)
      {
         printf("%d,%d,%d\n",p->Inf_No,p->Inf_Information,p->Inf_IsFill);
      }
   DeacheShm(pShmHead);
}
*/


//pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

int main()
{
   GetShm(shm_key,0664);
   AttacheShm(shm_id,NULL,0);
   //pShmTail = pShmHead+5;
   //pShmHead->Inf_Information = 0;
   //pShmHead->Inf_IsFill = 1;
   //pShmHead->Inf_No = 0;
    printf("head %p tail %p\n", pShmHead,pShmTail);
   //pthread_t thread;
   //if(pthread_create(&thread,NULL,routine,NULL)!=0)
   //   err_abort(errno,"pthread_create");
   //pthread_join(thread,NULL);
    while(1)
    ;  
    //DeacheShm(pShmHead);   
   
}

程序输出
head 0xb7f87000 tail (nil)

ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0xffffffff 1409025 xpston 664 60 1

第二次启动输出
head 0xffffffff tail (nil)

这种情况是因为什么原因产生的。求高手解答

[玉生香]

高手51都去玩了吗？ 自己顶起来