求共享内存的有关问题

求高手指点共享内存的问题
操作系统：64位redhat，想建立共享内存，代码如下：
  SHARE_MEM *share_mem_ptr = NULL;
  printf("\n create share mem\n");
int shmID = shmget(80045,sizeof(SHARE_MEM),IPC_CREAT+0666);
if(shmID<0) 
{
perror("shmget");
}
printf("===== SHMID %d\n", shmID);
share_mem_ptr = (SHARE_MEM *)shmat(shmID, 0, 0);
printf("\n shmat successful ptr %ld",share_mem_ptr);
perror("shmat");


执行结果如下： create share mem
  ===== QZH SHMID 213975121

shmat: Success
段错误 (core dumped)

请高手指点段错误是怎么回事~~~~


[解决办法]
确认key是合法的，不确认的话先调用ftok获取Key,如果返回-1，则调用creat创建文件，再次调用ftok获取Key，之后shmget。
[解决办法]

C/C++ code

SHARE_MEM *share_mem_ptr = NULL;  printf("\n create share mem\n");int shmID = shmget(80045,sizeof(SHARE_MEM),IPC_CREAT+0666);if(shmID<0) {perror("shmget");}printf("===== SHMID %d\n", shmID);share_mem_ptr = (SHARE_MEM *)shmat(shmID, 0, 0666|IPC_CREAT); //markprintf("\n shmat successful ptr %ld",share_mem_ptr);perror("shmat");
[解决办法]
给你个我自己的代码吧，运行木有问题的

C/C++ code
void *pshared_memory;int m_fd = shmget((key_t)m_key, nSize, IPC_CREAT|IPC_EXCL);    if(errno == EEXIST) //打开已存在共享内存    {        //printf("EEXIST\n");        m_fd = shmget((key_t)m_key, 0, 0);        if(m_fd == -1)        {            printf("there is some errors for this\n ");            assert(0);            m_pHead = DY_NULL;        }        else        {            pshared_memory = shmat(m_fd, 0, 0666);            m_pHead = (SSHheadInfo*)pshared_memory;            (m_pHead->nRefCount)++;        }        return;    }    pshared_memory = shmat(m_fd, 0, 0666|IPC_CREAT);
[解决办法]
段错误 (core dumped)

是指针出错了，是你上下文中有空指针出现了，或者写错了内存，现存的代码是没有问题的。【我只是加了if (shmctl(shmID, IPC_RMID, 0) < 0)
       err_sys("shmctl error");】

C/C++ code
main(void){    char* share_mem_ptr = NULL;  printf("\n create share mem\n");  int shmID = shmget(80045,64,IPC_CREAT+0666);  if(shmID<0)   {          perror("shmget");  }  printf("===== SHMID %d\n", shmID);  share_mem_ptr = (char *)shmat(shmID, 0, 0);  printf("\n shmat successful ptr %ld",share_mem_ptr);  perror("shmat");    if (shmctl(shmID, IPC_RMID, 0) < 0)        err_sys("shmctl error");    exit(0);}
[解决办法]
share_mem_ptr = (SHARE_MEM *)shmat(shmID, 0, 0);
改成
share_mem_ptr = (SHARE_MEM *)shmat(shmID, 0, 0666|IPC_CREAT);
[解决办法]
探讨


好像是shmget那个函数有问题，难道我指定的id：80045有问题吗？这个id如何指定啊，自己随便设一个不行吗