IPC 队列：- 接收错误数据

Question

如果 flag 设置为 0，我的程序在 msgrcv 函数上接收错误数据，但是，如果我将特定数据的 flag 设置为 1，则 msgrcv 函数将继续等待。我在公共文件中定义了发送和接收函数，并从发送者和接收者文件中调用它。我检查了调试数据，它已正确发送，但在接收端，如果标志设置为 0 意味着接收到第一个数据包，那么我收到了错误的数据。如果将 flag 设置为 1，则表示特定消息类型数据 msgrcv 函数以等待状态结束。请帮忙。 /CommonMsgQueue.c/

    int InitializeMsgQueue(char *keypath)
    {
       key_t key;
       int msgid;
       key = ftok(keypath,'B');
       if (key == -1 )
       {
          perror("Failed to generate key ");
          exit(0);
       }
       msgid = msgget(key, 0666 | IPC_CREAT );
       if ( msgid == -1 )
       {
          perror("Failed to get msgid");
          exit(0);
       }
       return msgid;
    }
    int SendMsg(key_t msgqid ,StMesgQ *MsgData , int msglength)
    {
        int iRetVal =0;
        iRetVal = msgsnd(msgqid,&MsgData,sizeof(StMesgQ),IPC_NOWAIT);
        if ( iRetVal == -1 )
        {
           perror("Failed to send message");
        }
        return iRetVal;
    }
    int RcvMsg(key_t msgqid, StMesgQ *MsgData , int msglength)
    {
       int iRetVal =0;
       iRetVal = msgrcv(msgqid,&MsgData,msglength,0,0);
       if (iRetVal == -1 )
       {
          perror("Failed to receive message ");
          exit(0);
       }
       
       return iRetVal;
    
    }
   /*Sender.c*/
   msgqid = InitializeMsgQueue("/home/nprabhat/Nitesh/Nitesh_FrameWork/Key/ClientQueue");
   CommonSHMData = (struct CommonSHM*)ShmData;
   StMesgQ obj;
   while (1)
   {
       
       printf("Sender:-- Enter the value For iIndex\n");
       scanf("%d",&value);
       CommonSHMData->iIndex = value;
       CommonSHMData->iIndex2 = value;
       DataPktToSend = (char*)CommonSHMData;
     memcpy(&obj.buf,&DataPktToSend,strlen(DataPktToSend));
       obj.iMsgType = 1;
       SendMsg(msgqid,&obj,sizeof(StMesgQ));
    }
  /*Reciever.c*/
  RcvMsg(msgqid,&MsgData,sizeof(StMesgQ));
  CommonSHMData_Recv = (struct CommonSHM*)MsgData.buf;
  printf("Data Received from queue is %d",CommonSHMData_Recv->iIndex);

Answer 1

关于：

   iRetVal = msgrcv( msgqid, &MsgData, msglength, 0, 0 );
   
   if (iRetVal == -1 )
   {
      perror("Failed to receive message ");
      exit(0);
   }
   
   memcpy(&MsgData,&RcvMsgData,sizeof(StMesgQ));

函数：memcpy()从右到左复制。

语法如下：

void *memcpy(void *destination, const void *source, size_t n);

因此，对memcpy() 的调用将通过对msgrcv() 的调用将放置在MsgData 中的数据与RcvMsgData 中恰好存在的任何垃圾覆盖在一起