1、服务器端实现

服务器端的主要功能是监听客户端连接，并将一个客户端发送的消息广播给所有连接的客户端。使用 socket() 创建套接字并绑定到指定端口。使用 accept() 等待客户端连接，每个连接创建一个线程来处理客户端。客户端发送的消息会被广播给所有其他已连接的客户端。

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

#define PORT 8080
#define MAX_CLIENTS 10
#define BUFFER_SIZE 1024

int client_sockets[MAX_CLIENTS];
pthread_mutex_t clients_mutex = PTHREAD_MUTEX_INITIALIZER;

void *handle_client(void *socket_desc) {
    int sock = *(int *)socket_desc;
    char buffer[BUFFER_SIZE];
    int read_size;

    while ((read_size = recv(sock, buffer, BUFFER_SIZE, 0)) > 0) {
        buffer[read_size] = '\0';
        printf("Client %d: %s\n", sock, buffer);

        // 广播消息给其他客户端
        pthread_mutex_lock(&clients_mutex);
        for (int i = 0; i < MAX_CLIENTS; i++) {
            if (client_sockets[i] != 0 && client_sockets[i] != sock) {
                send(client_sockets[i], buffer, strlen(buffer), 0);
            }
        }
        pthread_mutex_unlock(&clients_mutex);
    }

    // 客户端断开连接
    pthread_mutex_lock(&clients_mutex);
    for (int i = 0; i < MAX_CLIENTS; i++) {
        if (client_sockets[i] == sock) {
            client_sockets[i] = 0;
            break;
        }
    }
    pthread_mutex_unlock(&clients_mutex);

    close(sock);
    free(socket_desc);
    return 0;
}

int main() {
    int server_socket, client_socket, *new_sock;
    struct sockaddr_in server_addr, client_addr;
    socklen_t client_len = sizeof(struct sockaddr_in);

    // 创建服务器套接字
    server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket == -1) {
        printf("Could not create socket\n");
        return 1;
    }

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

    // 绑定套接字到地址
    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("Bind failed");
        return 1;
    }
    listen(server_socket, MAX_CLIENTS);

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

    while ((client_socket = accept(server_socket, (struct sockaddr *)&client_addr, &client_len))) {
        printf("Client connected: %d\n", client_socket);

        // 添加客户端到数组
        pthread_mutex_lock(&clients_mutex);
        for (int i = 0; i < MAX_CLIENTS; i++) {
            if (client_sockets[i] == 0) {
                client_sockets[i] = client_socket;
                break;
            }
        }
        pthread_mutex_unlock(&clients_mutex);

        // 为每个客户端创建一个新线程
        pthread_t client_thread;
        new_sock = malloc(sizeof(int));
        *new_sock = client_socket;
        if (pthread_create(&client_thread, NULL, handle_client, (void *)new_sock) < 0) {
            perror("Could not create thread");
            return 1;
        }

        pthread_detach(client_thread);
    }

    if (client_socket < 0) {
        perror("Accept failed");
        return 1;
    }

    close(server_socket);
    return 0;
}

2、客户端实现

客户端的主要功能是连接到服务器，并发送和接收消息。客户端首先需要连接到服务器，然后进入一个循环，等待用户输入消息并发送到服务器，同时接收并显示来自服务器的消息。使用 socket() 创建套接字并连接到服务器。使用一个线程不断接收服务器发送的消息，并在主线程中发送消息给服务器。

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

#define PORT 8080
#define BUFFER_SIZE 1024

void *receive_messages(void *socket_desc) {
    int sock = *(int *)socket_desc;
    char buffer[BUFFER_SIZE];
    int read_size;

    while ((read_size = recv(sock, buffer, BUFFER_SIZE, 0)) > 0) {
        buffer[read_size] = '\0';
        printf("%s", buffer);
    }

    return 0;
}

int main() {
    int client_socket;
    struct sockaddr_in server_addr;
    char message[BUFFER_SIZE];
    pthread_t receive_thread;

    // 创建客户端套接字
    client_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (client_socket == -1) {
        printf("Could not create socket\n");
        return 1;
    }

    // 设置服务器地址
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

    // 连接到服务器
    if (connect(client_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("Connect failed");
        return 1;
    }

    printf("Connected to server\n");

    // 创建接收消息的线程
    if (pthread_create(&receive_thread, NULL, receive_messages, (void *)&client_socket) < 0) {
        perror("Could not create thread");
        return 1;
    }

    // 发送消息到服务器
    while (fgets(message, BUFFER_SIZE, stdin) != NULL) {
        send(client_socket, message, strlen(message), 0);
    }

    close(client_socket);
    return 0;
}

3、编译运行

1）先编译运行服务器程序

gcc server.c -o server -pthread

./server

2）再编译运行多个客户端程序

gcc client.c -o client -pthread

./client