【C++网络编程】第2篇：简单的TCP服务器与客户端

一、TCP通信流程回顾

1. 服务器端流程

1. 创建Socket → socket()
2. 绑定地址和端口 → bind()
3. 开始监听 → listen()
4. 接受客户端连接 → accept()
5. 接收/发送数据 → recv()/send()
6. 关闭连接 → closesocket()

2. 客户端流程

1. 创建Socket → socket()
2. 连接服务器 → connect()
3. 发送/接收数据 → send()/recv()
4. 关闭连接 → closesocket()

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二、实现TCP服务器（Echo示例）​

1. 完整代码

#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h> 
#pragma comment(lib, "ws2_32.lib")  // 自动链接Winsock库

#include <ctype.h>
#include <limits.h>


int main() {
    // 1. 初始化Winsock
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
        std::cerr << "WSAStartup failed!" << std::endl;
        return 1;
    }

    // 2. 创建Socket
    SOCKET serverSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (serverSocket == INVALID_SOCKET) {
        std::cerr << "Socket creation failed: " << WSAGetLastError() << std::endl;
        WSACleanup();
        return 1;
    }

    // 3. 绑定地址和端口
    sockaddr_in serverAddr;
    serverAddr.sin_family = AF_INET;
    inet_pton(AF_INET,"127.0.0.1", &(serverAddr.sin_addr.s_addr));  // 本地回环地址
    serverAddr.sin_port = htons(8080);                    // 监听8080端口

    if (bind(serverSocket, (sockaddr*)&serverAddr, sizeof(serverAddr)) == SOCKET_ERROR) {
        std::cerr << "Bind failed: " << WSAGetLastError() << std::endl;
        closesocket(serverSocket);
        WSACleanup();
        return 1;
    }

    // 4. 开始监听
    if (listen(serverSocket, SOMAXCONN) == SOCKET_ERROR) {
        std::cerr << "Listen failed: " << WSAGetLastError() << std::endl;
        closesocket(serverSocket);
        WSACleanup();
        return 1;
    }

    std::cout << "Server started. Listening on 127.0.0.1:8080..." << std::endl;

    // 5. 接受客户端连接
    sockaddr_in clientAddr;
    int clientAddrLen = sizeof(clientAddr);
    SOCKET clientSocket = accept(serverSocket, (sockaddr*)&clientAddr, &clientAddrLen);
    if (clientSocket == INVALID_SOCKET) {
        std::cerr << "Accept failed: " << WSAGetLastError() << std::endl;
        closesocket(serverSocket);
        WSACleanup();
        return 1;
    }

    // 6. 接收并回传数据（Echo）
    char buffer[1024];
    int bytesReceived;
    do {
        bytesReceived = recv(clientSocket, buffer, sizeof(buffer), 0);
        if (bytesReceived > 0) {
            send(clientSocket, buffer, bytesReceived, 0);  // 原样返回数据
      
            std::cout << "Echoed " << bytesReceived << " bytes. Datas:" << std::string(buffer, bytesReceived) << std::endl;
        }
    } while (bytesReceived > 0);

    // 7. 清理资源
    closesocket(clientSocket);
    closesocket(serverSocket);
    WSACleanup();
    return 0;
}

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三、实现TCP客户端

1. 完整代码

#include <iostream>
#include <string>
#include <winsock2.h>
#include <ws2tcpip.h> 
#pragma comment(lib, "ws2_32.lib")

int main() {
    // 1. 初始化Winsock
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
        std::cerr << "WSAStartup failed!" << std::endl;
        return 1;
    }

    // 2. 创建Socket
    SOCKET clientSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (clientSocket == INVALID_SOCKET) {
        std::cerr << "Socket creation failed: " << WSAGetLastError() << std::endl;
        WSACleanup();
        return 1;
    }

    // 3. 连接服务器
    sockaddr_in serverAddr;
    serverAddr.sin_family = AF_INET;
    inet_pton(AF_INET, "127.0.0.1", &(serverAddr.sin_addr.s_addr));
    serverAddr.sin_port = htons(8080);

    if (connect(clientSocket, (sockaddr*)&serverAddr, sizeof(serverAddr)) == SOCKET_ERROR) {
        std::cerr << "Connect failed: " << WSAGetLastError() << std::endl;
        closesocket(clientSocket);
        WSACleanup();
        return 1;
    }

    std::cout << "Connected to server. Enter messages to send (type 'exit' to quit):" << std::endl;

    // 4. 发送和接收数据
    std::string message;
    char buffer[1024];
    do {
        std::getline(std::cin, message);
        if (message == "exit") break;

        // 发送数据
        send(clientSocket, message.c_str(), message.size(), 0);

        // 接收回显
        int bytesReceived = recv(clientSocket, buffer, sizeof(buffer), 0);
        if (bytesReceived > 0) {
            std::cout << "Server echoed: " << std::string(buffer, bytesReceived) << std::endl;
        }
    } while (true);

    // 5. 清理资源
    closesocket(clientSocket);
    WSACleanup();
    return 0;
}

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四、关键代码解析

1. socket() 参数说明

• AF_INET：IPv4地址族。
• SOCK_STREAM：面向流的传输协议（TCP）。
• IPPROTO_TCP：明确指定TCP协议（可填0自动选择）。

2. bind() 的地址设置

• INADDR_ANY：若服务器需要监听所有网卡，可改为：

serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);  // 监听所有网卡

3. listen() 的待处理队列

• SOMAXCONN：系统允许的最大挂起连接数（Windows默认为200）。

4. accept() 的阻塞特性

• 若无客户端连接，accept()会一直阻塞，直到新连接到达。

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五、运行与测试

1. 客户端输入/输出

2. 服务器端输出