用宏定义的形式书写代码块

  今天读一个ip传输文件的小例子，看到一个宏定义是这样的：

#define TimeBlock(_out, _block) \
    struct timeval start; \
    struct timeval end; \
    struct timeval delta; \
    gettimeofday(&start, NULL); \
    _block \
    gettimeofday(&end, NULL); \
    timersub(&end, &start, &delta); \
    fprintf(_out, "%lu\n", (delta.tv_sec * 1000000L) + delta.tv_usec);

  当时感觉好奇怪啊，从没见过这样的书写形式，在论坛问了一下，原来这是一个宏定义的函数，这个函数有两个参数，一个是_out,一个是_block，其中_out是输出，_block是代码块，该函数首先创建3个timeval结构体，然后读取当前时间作为代码块开始时间，执行代码块，读取当前时间作为结束时间，计算代码块执行时间并输出。

  具体的宏定义应用如下所示：

    TimeBlock(stdout, {
        if ((socketfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
            LogFatal("socket() failed");
        }

        memset(&serverAddress, 0, sizeof(serverAddress));
        serverAddress.sin_family = AF_INET;
        serverAddress.sin_addr.s_addr = inet_addr(serverIPAddress);
        serverAddress.sin_port = htons(serverPort);

        int on = 1;
        if (setsockopt(socketfd, SOL_SOCKET, SO_REUSEADDR, (const char *) &on, sizeof(on)) < 0) {
            LogFatal("setsockopt() failed");
        }

        if (connect(socketfd, (struct sockaddr *) &serverAddress, sizeof(serverAddress)) < 0) {
            LogFatal("connect() failed");
        }

        fileNameLen = strlen(fileName);

        if (send(socketfd, fileName, fileNameLen, 0) != fileNameLen) {
            LogFatal("send() sent a different number of bytes than expected");
        }

        totalBytesRcvd = 0;
#if DEBUG
        fprintf(stderr, "Received: \n");
#endif
        for (;;) {

            bytesReceived = recv(socketfd, serverResponseBuffer, RCVBUFSIZE, 0);
            totalBytesRcvd += bytesReceived;

            // printf("%.*s", bytesReceived, serverResponseBuffer);

            if (bytesReceived < RCVBUFSIZE) {
                break;
            }
        }

#if DEBUG
        fprintf(stderr, "\n");
#endif

        close(sock);
    });