用select检测socket是否”ready”

    1. struct fd_set rdfs;
    2. struct timeval tv = {5 , 0};   // 设置5秒时间
    3. while
    4. {
    5.     FD_ZERO(&rdfs);
    6.     FD_SET(sockfd, &rdfs);
    8.     if (select(sockfd+1, &rdfs, NULL, NULL, &tv) > 0)   // socket就绪
    9.     {
    10.         recv() /  recvfrom()    //  从socket读取数据
    11.     }
    12. }