C语言中如何进行网络编程 C语言socket通信基础与示例

#include <fcntl.h>
#include <unistd.h>

int flags = fcntl(client_socket, F_GETFL, 0);
if (flags == -1) {
    perror("fcntl F_GETFL failed");
    exit(EXIT_FAILURE);
}

flags |= O_NONBLOCK;
if (fcntl(client_socket, F_SETFL, flags) == -1) {
    perror("fcntl F_SETFL failed");
    exit(EXIT_FAILURE);
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT 8080
#define MAX_CLIENTS 30

int main() {
    int server_fd, new_socket, client_sockets[MAX_CLIENTS], max_clients = MAX_CLIENTS;
    struct sockaddr_in address;
    int addrlen = sizeof(address);
    fd_set readfds;

    // 初始化client_sockets数组
    for (int i = 0; i < max_clients; i++) {
        client_sockets[i] = 0;
    }

    // 创建服务器Socket
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

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

    // 绑定Socket到指定端口
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 监听连接
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    printf("Listening on port %d\n", PORT);

    while (1) {
        // 清空Socket集合
        FD_ZERO(&readfds);

        // 添加服务器Socket到集合
        FD_SET(server_fd, &readfds);
        int max_sd = server_fd;

        // 添加客户端Sockets到集合
        for (int i = 0; i < max_clients; i++) {
            int sd = client_sockets[i];
            if (sd > 0) {
                FD_SET(sd, &readfds);
            }
            if (sd > max_sd) {
                max_sd = sd;
            }
        }

        // 使用select等待Socket活动
        int activity = select(max_sd + 1, &readfds, NULL, NULL, NULL);

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

        // 如果服务器Socket有活动，说明有新的连接
        if (FD_ISSET(server_fd, &readfds)) {
            if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
                perror("accept");
                exit(EXIT_FAILURE);
            }

            printf("New connection , socket fd is %d , ip is : %s , port : %d\n", new_socket, inet_ntoa(address.sin_addr), ntohs(address.sin_port));

            // 将新的Socket添加到client_sockets数组
            for (int i = 0; i < max_clients; i++) {
                if (client_sockets[i] == 0) {
                    client_sockets[i] = new_socket;
                    printf("Adding to list of sockets as %d\n", i);
                    break;
                }
            }
        }

        // 处理客户端Sockets
        for (int i = 0; i < max_clients; i++) {
            int sd = client_sockets[i];

            if (FD_ISSET(sd, &readfds)) {
                char buffer[1024] = {0};
                int valread;
                if ((valread = read(sd, buffer, 1024)) == 0) {
                    // 客户端断开连接
                    getpeername(sd, (struct sockaddr*)&address, (socklen_t*)&addrlen);
                    printf("Host disconnected , ip %s , port %d \n", inet_ntoa(address.sin_addr), ntohs(address.sin_port));

                    close(sd);
                    client_sockets[i] = 0;
                } else {
                    // 处理客户端发送的数据
                    buffer[valread] = '\0';
                    printf("Received from client %d: %s\n", sd, buffer);
                    send(sd, buffer, strlen(buffer), 0); // Echo back the message
                }
            }
        }
    }

    return 0;
}