从SHMAT

Question

我使用shmget和shmat创建一个读写缓冲区。但是，当我写写段时，我的程序崩溃了。这是代码-

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



void Cds_shminit(unsigned int key, unsigned int size, void* shmp)
{

  int shmid;
  shmid = shmget(key, size, 0644|IPC_CREAT);
  if(shmid == -1){
    printf("AICM_DEBUG(TCL Process):Error allocating shared memory...\n");
    exit(-1);
  }

  /*if the shared memory assignment is successful, attach to the segment
and obtain a pointer*/
  shmp = shmat(shmid, NULL, 0);
  if(shmp == (void *) -1){
    printf("AICM_DEBUG(TCL Process):Error attaching to shared memory....\n");
  }


}


int main(void)
{
  int shmid1,shmid2;
  void *p;
  void *q;

  Cds_shminit(0x1234, 1024, p);
  if(p==NULL){
    printf("Null Ptr p\n");
  }
  int a = 0x51515151;
  int *u;
  u = (int *)p;
  *u = a;

 Cds_shminit(0x1234, 1024, q);
 if(q==NULL){
   printf("Null Ptr q\n");
 }
 printf("%x \n",*(int *)q);
 printf ("%x %x\n",p,q);

 while(1);
}

最后，我添加了检查以查看p是否为NULL，并且确实如此。有人可以帮我找到此代码的问题吗？如果我全局声明了void指针（在main（）外部声明void * p和void * q）。我无法投下他们。强制转换全局空指针是否有限制？