do{ ;}while(false)技巧揭密

 

do
    {
        ZeroMemory(szProtoBuffer, sizeof(szProtoBuffer));

        pMsgHdr = ( PNFS_MSG_HEADER )szProtoBuffer ;

        ZeroMemory( pMsgHdr , sizeof( NFS_MSG_HEADER )) ;

        pMsgHdr->dwSignature = RNFS_MAGIC ;
        pMsgHdr->wProtocolVersion = RNFS_PROTOVERSION ;
        pMsgHdr->btPacketType = RNFS_DGRAM_REQUEST ;
        pMsgHdr->dwPacketLength = 0 ;
        pMsgHdr->wFunctionNum = RNFS_OPEN_SESSION ;
        pMsgHdr->dwAckNumber = dwAckNumber ;

        dwSize = MSG_HDR_LEN + pMsgHdr->dwPacketLength ;

        dwStatus = GU_SendAll(
                        SessionSocket ,
                        szProtoBuffer ,
                        dwSize ) ;
        if( 0 != dwStatus )
        {
            break ;
        }

        dwSize = MSG_HDR_LEN ;

        dwStatus = GU_RecvAll(
                        SessionSocket ,
                        szProtoBuffer,
                        dwSize ) ;
        if( 0 != dwStatus )
        {
            break ;
        }

        if( pMsgHdr->dwAckNumber != dwAckNumber )
        {
            dwStatus = ERROR_BAD_FORMAT ;
            break ;
        }
        
        if( pMsgHdr->dwRetStatus != 0 )
        {
            dwStatus = pMsgHdr->dwRetStatus ;
            break ;
        }

        dwSize = pMsgHdr->dwPacketLength ;

        dwStatus = GU_RecvAll(
                        SessionSocket ,
                        szProtoBuffer ,
                        dwSize ) ;
        if( 0 == dwStatus )
        {
            PNFS_SESSION pSession = ( PNFS_SESSION )szProtoBuffer ;
            * pdwSessionId = pSession->dwSessionId ;
        }
    } while( FALSE ) ;

 

开始觉得不是多此一举吗？仔细分析了以后，才发现很妙，因为在不同的条件判断中就可以按需break;从而达到最终执行到最后一个返回语句。而以前的实现都是以goto来实现的。