用宏定义的形式书写代码块

来源：互联网发布：抽风解说知乎编辑：程序博客网时间：2024/06/10 13:58

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);    });

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