刚开始学c语言，不会写

Question

有abc三个client，给他标记id，每一个client可以指定发送消息给任意一个client，c语言，这个服务端代码如何写

Answer 1

以下是一个用C语言编写的简单的服务器代码，可以处理来自三个客户端的消息，并相应地将消息发送给指定的客户端。

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

#define MAX_CLIENTS 3

int clients[MAX_CLIENTS];
pthread_t threads[MAX_CLIENTS];
int active_clients = 0;

typedef struct {
    int client_id;
    char message[256];
} Message;

// 处理客户端消息的线程函数
void* handle_client(void* arg) {
    int client_id = *((int*) arg);
    int client_socket = clients[client_id];
    Message message;

    while (1) {
        memset(&message, 0, sizeof(Message));

        // 从客户端接收消息
        ssize_t bytes_received = recv(client_socket, &message, sizeof(Message), 0);
        if (bytes_received <= 0) {
            // 客户端断开连接
            break;
        }

        // 查找指定接收者的客户端
        int recipient_id = message.client_id;
        int recipient_socket = clients[recipient_id];

        // 发送消息给指定的客户端
        ssize_t bytes_sent = send(recipient_socket, &message, sizeof(Message), 0);
        if (bytes_sent <= 0) {
            // 发送失败，可能客户端断开连接或出现错误
            break;
        }
    }

    // 关闭客户端连接
    close(client_socket);
    clients[client_id] = 0;
    active_clients--;

    return NULL;
}

int main() {
    int server_socket, client_socket;
    struct sockaddr_in server_address, client_address;
    socklen_t client_address_length = sizeof(client_address);

    // 创建服务器socket
    server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket < 0) {
        perror("Failed to create socket");
        exit(1);
    }

    // 设置服务器地址
    server_address.sin_family = AF_INET;
    server_address.sin_port = htons(8888);
    server_address.sin_addr.s_addr = INADDR_ANY;

    // 绑定服务器socket到指定地址和端口
    if (bind(server_socket, (struct sockaddr*) &server_address, sizeof(server_address)) < 0) {
        perror("Failed to bind socket");
        exit(1);
    }

    // 监听客户端连接
    if (listen(server_socket, 3) < 0) {
        perror("Failed to listen for connections");
        exit(1);
    }

    printf("Server started. Waiting for clients...\n");

    // 等待客户端连接
    while (active_clients < MAX_CLIENTS) {
        // 接受客户端连接
        client_socket = accept(server_socket, (struct sockaddr*) &client_address, &client_address_length);
        if (client_socket < 0) {
            perror("Failed to accept connection");
            exit(1);
        }

        // 在clients数组中找到一个空闲位置
        int client_id = 0;
        while (clients[client_id] != 0) {
            client_id++;
        }

        // 将新的客户端socket保存在clients数组中
        clients[client_id] = client_socket;
        active_clients++;

        // 创建新的线程来处理客户端消息
        if (pthread_create(&threads[client_id], NULL, handle_client, &client_id) != 0) {
            perror("Failed to create thread");
            exit(1);
        }

        printf("Client %d connected\n", client_id);
    }

    // 等待所有客户端线程结束
    for (int i = 0; i < MAX_CLIENTS; i++) {
        if (threads[i]) {
            pthread_join(threads[i], NULL);
        }
    }

    // 关闭服务器socket
    close(server_socket);

    return 0;
}