检查特定客户端（使用 ip1，port1）是否连接到套接字？答案

【问题标题】：check whether a particular client (with ip1, port1) is connected to socket or not?检查特定客户端（使用 ip1，port1）是否连接到套接字？
【发布时间】：2014-12-20 08:49:49
【问题描述】：

这是一个基于 UDP 的基本客户端服务器程序。如果客户端 1 发送数据客户端 2 将接收，反之亦然。

address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons( PORT );

//bind the socket to localhost port 1902
if (bind(master_socket, (struct sockaddr *)&address, sizeof(address))<0) 
{
    perror("bind failed");
    exit(EXIT_FAILURE);
}
printf("Listener on port %d \n", PORT);


if (listen(master_socket, 3) < 0)
{
    perror("listen");
    exit(EXIT_FAILURE);
}

//accept the incoming connection
addrlen = sizeof(address);
puts("Waiting for connections ...");

while(TRUE) 
{
    //clear the socket set
    FD_ZERO(&readfds);

    //add master socket to set
    FD_SET(master_socket, &readfds);
    max_sd = master_socket;

    //add child sockets to set
    for ( i = 0 ; i < max_clients ; i++) 
    {
        //socket descriptor
        sd = client_socket[i];

        //if valid socket descriptor then add to read list
        if(sd > 0)
            FD_SET( sd , &readfds);

        //highest file descriptor number, need it for the select function
        if(sd > max_sd)
            max_sd = sd;
    }

    //wait for an activity on one of the sockets , timeout is NULL , so wait indefinitely
    activity = select( max_sd + 1 , &readfds , NULL , NULL , NULL);

    if ((activity < 0) && (errno!=EINTR)) 
    {
        printf("select error");
    }

    //If something happened on the master socket , then its an incoming connection
    if (FD_ISSET(master_socket, &readfds)) 
    {
        if ((new_socket = accept(master_socket, (struct sockaddr *)&address, (socklen_t*)&addrlen))<0)
        {
            perror("accept");
            exit(EXIT_FAILURE);
        }

        //inform user of socket number - used in send and receive commands
        printf("New connection , socket fd is %d , ip is : %s , port : %d \n" , new_socket , inet_ntoa(address.sin_addr) , ntohs(address.sin_port));

    ....
    ....
    //what has to be done here to check a client with IP1, Port 1 is already connected? //
    ....
    ....
    }

    }

在这个程序中，我收到一条消息

New connection , socket fd is 4 , ip is : 127.0.0.1 , port : 44851 
Welcome message sent successfully
Adding to list of sockets as 0
New connection , socket fd is 5 , ip is : 127.0.0.1 , port : 44852 
Welcome message sent successfully
Adding to list of sockets as 1

收到此消息后，我想检查是否连接了具有 IP1、端口 1 的特定客户端？例如检查 ip 127.0.0.1 和端口 44852 的客户端是否已经连接？如果已连接打印，则所需的客户端已经可用。任何人都可以建议我这样做吗？

【问题讨论】：

您说您使用的是 UDP，但此代码用于 TCP。您不能将 listen() 和 accept() 与 UDP 一起使用。

标签： sockets udp ip

【解决方案1】：

如何做到这一点应该很明显。您将客户信息存储在列表中。因此，只需遍历列表，检查accept() 报告的 ip/port 是否已经在列表中，如果没有则添加。只要确保在客户端断开连接时保持列表是最新的。

【讨论】：