#include "stdio.h"
#include "sys/types.h"
#include "errno.h"
#include "sys/shm.h"
#include "sys/ipc.h"
#include "string.h"
#include "sys/sem.h"
#include "unistd.h"


#define K    1024
#define SHMSIZE K*4*16
#define SHMFLAGS IPC_CREAT|0644

struct mystruct{
  int user_name;
  struct mystruct * next;
};

typedef struct mystruct * MYSTRUCT;


int shmid;
cleanup(){
   shmctl(shmid,IPC_RMID,0);
   exit(0);
}


main(){
  char * addr1;
  int i;
  pid_t pid;

  MYSTRUCT user_struct;
  MYSTRUCT p,q,r;


  for(i=0;i<20;i++)
   signal(i,cleanup);

  shmid = shmget(IPC_PRIVATE,SHMSIZE,SHMFLAGS);

  if(shmid == -1){
   printf("shm create failed!\n");

  }else{
   printf("shared memory segment ID = %d\n",shmid);
   addr1 = shmat(shmid,0,0);

if((pid=fork())==0){
        user_struct = (MYSTRUCT)addr1;
        r = user_struct;
        i=0;

  while(i<100){
/*      q=(MYSTRUCT)malloc(sizeof(struct mystruct));
*/
      q=user_struct++;
      q->user_name = i;
      q->next=NULL;
      r->next=q;
      r=r->next;
      i++;
   
/*      sleep(1);     */
/*
此处如果不加sleep(1),则一切正常，如果加上sleep(1),
那么仅仅打印链表的第一二个节点的地址，等很久以后，
可能会打印以后节点的地址，是不是由于进程不同步的问题？
*/


  }      
}
   if((pid=fork())==0){
   while(1){   
      p= (MYSTRUCT)addr1;
           i=0;    
      while(p!=NULL){
         printf("0x%x\n",p);   
         p=p->next;
 
i++;
      }
      sleep(2);
   }
   }
   shmdt(addr1);

   shmctl(shmid,IPC_RMID,0);
  }   

}