TCP/IP 编程

1. 探测链接是否存活选项:  SO_KEEPALIVE， 默认关闭linux     打开：缓存 int optval = 1;setsockopt(clifd, SOL_SOCKET, SO_KEEPALIVE, (char *)&optval, sizeof(optval))；socket 默认2小时发送一次探测包code 2. 探测接收缓存中可读的字节数:  io unsigned int

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