Reader不是从共享内存中读取的

Question

我正在从一个文件中读取然后将其写在共享内存上。但是Writer在共享内存中写入工作正常但读者不是从共享内存中读取。 maxlen [x]存储了一条线的最大长度。

void * reader (void * param){
  int i;
  int count=1;
  int waittime;

  waittime = rand() % 5;
  sleep(waittime);   
  shm_ptr = shmat(shm_id, NULL, 0); 

  if ((int)shm_ptr == -1){
      printf("*** shmat error (server) ***\n");
      exit(1);   
  }

  sleep(1);
  printf("\nReader is trying to enter");
  sem_wait(&mutex);
  readcount++;

  if(readcount==1) 
    sem_wait(&wrt);

  printf("\n%d Reader is inside ",readcount);
  printf(" in crtical section \n");
  int sizes=x;
  x=0;

  while (x<=sizes) {   
   shm_ptr[x] =  malloc( sizeof(char *)* maxlen[x]);
   puts(shm_ptr[x]);
   x++;   
  }

  sem_post(&mutex);
  sem_wait(&mutex);
  readcount--;

  if(readcount==0)
      sem_post(&wrt);

  sem_post(&mutex);
  printf("\nReader is Leaving");
  sleep(waittime);
}