C/C++设计高并发访问：多客户端并发访问服务器 服务器端和客户端 代码

这个问题涉及到的知识点比较广泛，需要包括网络编程、并发编程等方面的内容。

首先，服务器端需要创建一个监听套接字，并绑定到指定的IP地址和端口上，然后通过调用listen函数将该套接字设置为监听状态。

接着，服务器端需要采用多线程或多进程的方式，对于每个新的客户端连接，都创建一个新的线程或进程来处理，避免单线程或单进程的情况下，一个客户端的阻塞操作会影响到其他客户端的正常访问。

在服务器端线程或进程中，需要通过accept函数接收客户端的连接请求，并获得与该客户端通信的套接字，然后将该套接字交给一个新的线程或进程来处理客户端请求。

对于客户端，需要创建一个套接字，并向服务器端发起连接请求。如果连接成功，则可以通过send和recv函数与服务器端进行数据交换。

下面是一个简单的C++实现：

服务器端代码：

#include <iostream>
#include <cstring>
#include <thread>
#include <mutex>
#include <vector>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

std::mutex mtx;

void handle_client(int client_socket) {
    // 处理客户端请求
    char buffer[1024];
    while(true) {
        memset(buffer, 0, sizeof(buffer));
        int ret = recv(client_socket, buffer, sizeof(buffer), 0);
        if(ret <= 0) {
            break;
        }
        std::cout << "Receive message from client: " << buffer << std::endl;
        std::string reply = "Hello, I am server!";
        send(client_socket, reply.c_str(), reply.size(), 0);
    }
    close(client_socket);
}

void start_server(int port) {
    // 创建监听套接字
    int server_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if(server_socket < 0) {
        std::cerr << "Create socket failed!" << std::endl;
        return;
    }
    // 绑定IP地址和端口
    struct sockaddr_in server_addr;
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(port);
    int ret = bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));
    if(ret < 0) {
        std::cerr << "Bind socket failed!" << std::endl;
        close(server_socket);
        return;
    }
    // 监听
    ret = listen(server_socket, 10);
    if(ret < 0) {
        std::cerr << "Listen socket failed!" << std::endl;
        close(server_socket);
        return;
    }
    std::cout << "Server start listening on port " << port << " ..." << std::endl;
    // 处理客户端请求
    while(true) {
        struct sockaddr_in client_addr;
        socklen_t client_addrlen = sizeof(client_addr);
        int client_socket = accept(server_socket, (struct sockaddr*)&client_addr, &client_addrlen);
        if(client_socket < 0) {
            std::cerr << "Accept socket failed!" << std::endl;
            continue;
        }
        std::cout << "Accept client connection from " << inet_ntoa(client_addr.sin_addr) << ":" << ntohs(client_addr.sin_port) << std::endl;
        std::thread th(handle_client, client_socket);
        th.detach();
    }
    close(server_socket);
}

int main() {
    int port = 9000;
    start_server(port);
    return 0;
}

客户端代码：

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

int main() {
    // 创建套接字
    int client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if(client_socket < 0) {
        std::cerr << "Create socket failed!" << std::endl;
        return -1;
    }
    // 连接服务器
    struct sockaddr_in server_addr;
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    server_addr.sin_port = htons(9000);
    int ret = connect(client_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));
    if(ret < 0) {
        std::cerr << "Connect server failed!" << std::endl;
        close(client_socket);
        return -1;
    }
    std::cout << "Connect server success!" << std::endl;
    // 发送和接收数据
    std::string message = "Hello, I am client!";
    send(client_socket, message.c_str(), message.size(), 0);
    char buffer[1024];
    memset(buffer, 0, sizeof(buffer));
    ret = recv(client_socket, buffer, sizeof(buffer), 0);
    std::cout << "Receive message from server: " << buffer << std::endl;
    // 关闭套接字
    close(client_socket);
    return 0;
}