编写一个C语言基于TCP协议的网络通信程序，要求服务器通过套接字连接后，要求输入用户名，判断用户名正确后，向客户端发送连接正确的字符串，在服务器显示客户端的IP地址和端口。

好的，我会为您提供一个简单的C语言基于TCP协议的网络通信程序。

服务器端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define PORT 8888
#define MAX_CLIENTS 5

int main(int argc, char *argv[]) {
    int server_socket, client_socket, max_sd, activity, i;
    struct sockaddr_in server_addr, client_addr;
    char buffer[1024];

    // 创建TCP套接字
    if ((server_socket = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置服务器地址和端口
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);

    // 绑定套接字到指定地址和端口
    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 监听客户端连接
    if (listen(server_socket, MAX_CLIENTS) < 0) {
        perror("listen failed");
        exit(EXIT_FAILURE);
    }

    printf("Server is listening on port %d\n", PORT);

    // 接受客户端连接并处理请求
    while (1) {
        fd_set read_fds;
        FD_ZERO(&read_fds);
        FD_SET(server_socket, &read_fds);
        max_sd = server_socket;

        // 添加活动套接字到集合中
        for (i = 0; i < MAX_CLIENTS; i++) {
            client_socket = client_sockets[i];
            if (client_socket > 0) {
                FD_SET(client_socket, &read_fds);
            }
            if (client_socket > max_sd) {
                max_sd = client_socket;
            }
        }

        // 等待活动套接字
        activity = select(max_sd + 1, &read_fds, NULL, NULL, NULL);
        if ((activity < 0) && (errno != EINTR)) {
            perror("select error");
        }

        // 如果是新的连接请求，接受连接并添加到客户端套接字数组
        if (FD_ISSET(server_socket, &read_fds)) {
            int addrlen = sizeof(client_addr);
            if ((client_socket = accept(server_socket, (struct sockaddr *)&client_addr, (socklen_t *)&addrlen)) < 0) {
                perror("accept failed");
                exit(EXIT_FAILURE);
            }

            printf("New client connected from %s:%d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));

            // 向客户端发送连接成功消息
            char *message = "Connection established. Please enter your username:\n";
            if (send(client_socket, message, strlen(message), 0) != strlen(message)) {
                perror("send failed");
            }

            // 添加新的套接字到客户端套接字数组
            for (i = 0; i < MAX_CLIENTS; i++) {
                if (client_sockets[i] == 0) {
                    client_sockets[i] = client_socket;
                    break;
                }
            }
        }

        // 处理客户端请求
        for (i = 0; i < MAX_CLIENTS; i++) {
            client_socket = client_sockets[i];
            if (FD_ISSET(client_socket, &read_fds)) {
                int valread;
                if ((valread = read(client_socket, buffer, 1024)) == 0) {
                    // 客户端关闭连接
                    printf("Client disconnected from %s:%d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
                    close(client_socket);
                    client_sockets[i] = 0;
                } else {
                    // 处理客户端请求
                    buffer[valread - 1] = '\0'; // 去掉末尾的换行符
                    printf("%s:%d - %s\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), buffer);
                    // 判断用户名是否正确并发送结果
                    if (strcmp(buffer, "username") == 0) {
                        char *message = "Username is correct.\n";
                        if (send(client_socket, message, strlen(message), 0) != strlen(message)) {
                            perror("send failed");
                        }
                    } else {
                        char *message = "Username is incorrect.\n";
                        if (send(client_socket, message, strlen(message), 0) != strlen(message)) {
                            perror("send failed");
                        }
                    }
                }
            }
        }
    }

    return 0;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define SERVER_IP "127.0.0.1"
#define PORT 8888

int main(int argc, char *argv[]) {
    int server_socket;
    struct sockaddr_in server_addr;
    char buffer[1024];

    // 创建TCP套接字
    if ((server_socket = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置服务器地址和端口
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    if (inet_pton(AF_INET, SERVER_IP, &server_addr.sin_addr) <= 0) {
        perror("inet_pton failed");
        exit(EXIT_FAILURE);
    }

    // 连接服务器
    if (connect(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("connect failed");
        exit(EXIT_FAILURE);
    }

    // 接收连接成功消息并输入用户名
    int valread;
    if ((valread = read(server_socket, buffer, 1024)) > 0) {
        printf("%s", buffer);
        fgets(buffer, 1024, stdin);
        if (send(server_socket, buffer, strlen(buffer), 0) != strlen(buffer)) {
            perror("send failed");
        }
    }

    // 接收用户名判断结果并输出
    if ((valread = read(server_socket, buffer, 1024)) > 0) {
        printf("%s", buffer);
    }

    close(server_socket);

    return 0;
}

运行服务器端程序后，运行客户端程序并输入用户名，即可看到服务器端输出客户端的IP地址和端口，并发送用户名判断结果。