共享內存

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

#define BUFFER_SIZE 2048

int main()
{
 pid_t pid;
 int shmid;
 char *shm_addr;
 char flag[] = "WROTE";
 char buff[BUFFER_SIZE];

 if((shmid = shmget(IPC_PRIVATE,BUFFER_SIZE,0666))<0)   //創建共享內存
 {
  perror("shmget");
  exit(0);
 }
 else
 {
  printf("Create share-memory: %d/n",shmid);
 }
 
 system("ipcs -m");   //顯示共享內存情況  shell命令
 
 pid = fork();   //創建子進程
 if(pid == -1)
 {
  perror("fork");
  exit(1);
 }
 else if(pid == 0)    //子進程處理
 {
  if((shm_addr = shmat(shmid,0,0)) == (void*)-1)    //映射共享內存
  {
   perror("Child:shmat");
   exit(1);
  }
  else
  {
   printf("Child:Attach share-memory:%p/n",shm_addr);
  }

  system("ipcs -m");

 

/*通過檢查在共享內存的頭部是否有標誌字符串WROTE來確認

父進程已經向共享內存寫入有效數據*/
  
  while(strncmp(shm_addr,flag,strlen(flag)))
  {
   printf("Child:Wait for enable data.../n");
   sleep(5);
  }
  
  strcpy(buff,shm_addr + strlen(flag));    //獲取共享內存的有效數據並顯示
  printf("Child:Share-memory: %s/n",buff);
  
  if((shmdt(shm_addr)) < 0)     //解除共享內存映射
  {
   perror("shmdt");
   exit(1);
  }
  else
  {
   printf("Child:Deattach shared-memory/n");
  }

  system("ipcs -m");
  
  if(shmctl(shmid,IPC_RMID,NULL) == -1)   //刪除共享內存
  {
   perror("Child:shmctl(IPC_RMID)/n");
   exit(1);
  }
  else
  {
   printf("Delete share-memory/n");
  }
  
  system("ipcs -m");
 }
 else    //父進程處理
 {
  if((shm_addr = shmat(shmid,0,0)) == (void*)-1)    //映射共享內存
  {
   perror("Parent: shmat");
   exit(1);
  }
  else
  {
   printf("Parent:Attach shared-memory: %p/n",shm_addr);
  }
  sleep(1);
  printf("/nInput some string:/n");
  fgets(buff,BUFFER_SIZE,stdin);
  strncpy(shm_addr + strlen(flag),buff,strlen(buff));
  strncpy(shm_addr,flag,strlen(flag));
  
  if((shmdt(shm_addr))<0)    //解除共享內存映射
  {
   perror("Parent:shmdt");
   exit(1);
  }
  else
  {
   printf("Parent:Deattach shared-memory/n");
  }
  
  system("ipcs -m");
  
  waitpid(pid,NULL,0);
  printf("Finished/n");
 }
 exit(0);
}