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WinsockWSADATA wsaData;if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {std::cerr << "WSAStartup failed!" << std::endl;return 1;}// 2. 创建SocketSOCKET 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WinsockWSADATA wsaData;if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {std::cerr << "WSAStartup failed!" << std::endl;return 1;}// 2. 创建SocketSOCKET 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