【原创】网络编程中select函数的教训

先看一代码:

    fd_set readfs,writefs;

    int maxfd = -1;

    struct timeval tp;

    int nret  = 0;

    unchar brcvbuf[2048];

    tp.tv_sec = 2;

    tp.tv_usec = 0;

    FD_ZERO(&readfs);

    FD_ZERO(&writefs);

    FD_SET(g_isockid, &readfs);   /* g_isockid 为要检测的socket*/

    maxfd = Max(maxfd, g_isockid);

    maxfd += 1;

    nret = select(maxfd, &readfs, &writefs, NULL, &tp);

    if (FD_ISSET(g_isockid, &readfs))  /*判断是否有数据*/

    {

        ndsize = recv(g_isockid, brcvbuf, sizeof(brcvbuf), 0);

    }

 

昨眼一看没什么大问题,但select在每个操作系统的表现不太一样，比如在HP下，就有可能没有数据但执行到recv的情况！！！

所有调用select时，必须要检测其返回值！！

上面代码修改如下：

    fd_set readfs,writefs;

    int maxfd = -1;

    struct timeval tp;

    int nret  = 0;

    unchar brcvbuf[2048];

    tp.tv_sec = 2;

    tp.tv_usec = 0;

    FD_ZERO(&readfs);

    FD_ZERO(&writefs);

    FD_SET(g_isockid, &readfs);   /* g_isockid 为要检测的socket*/

    maxfd = Max(maxfd, g_isockid);

    maxfd += 1;

    nret = select(maxfd, &readfs, &writefs, NULL, &tp);

    if(nret < 0) 

    {

        return;

    }

    if (FD_ISSET(g_isockid, &readfs))  /*判断是否有数据*/

    {

        ndsize = recv(g_isockid, brcvbuf, sizeof(brcvbuf), 0);

    }