一、TCP通信流程回顧

1. 服務器端流程

1. 創建Socket → socket()
2. 綁定地址和端口 → bind()
3. 開始監聽 → listen()
4. 接受客戶端連接 → accept()
5. 接收/發送數據 → recv()/send()
6. 關閉連接 → closesocket()

2. 客戶端流程

1. 創建Socket → socket()
2. 連接服務器 → connect()
3. 發送/接收數據 → send()/recv()
4. 關閉連接 → closesocket()

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二、實現TCP服務器（Echo示例）?

1. 完整代碼

#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h> 
#pragma comment(lib, "ws2_32.lib")  // 自動鏈接Winsock庫#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. 創建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. 綁定地址和端口sockaddr_in serverAddr;serverAddr.sin_family = AF_INET;inet_pton(AF_INET,"127.0.0.1", &(serverAddr.sin_addr.s_addr));  // 本地回環地址serverAddr.sin_port = htons(8080);                    // 監聽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. 開始監聽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. 接受客戶端連接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. 接收并回傳數據（Echo）char buffer[1024];int bytesReceived;do {bytesReceived = recv(clientSocket, buffer, sizeof(buffer), 0);if (bytesReceived > 0) {send(clientSocket, buffer, bytesReceived, 0);  // 原樣返回數據std::cout << "Echoed " << bytesReceived << " bytes. Datas:" << std::string(buffer, bytesReceived) << std::endl;}} while (bytesReceived > 0);// 7. 清理資源closesocket(clientSocket);closesocket(serverSocket);WSACleanup();return 0;
}

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三、實現TCP客戶端

1. 完整代碼

#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. 創建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. 連接服務器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. 發送和接收數據std::string message;char buffer[1024];do {std::getline(std::cin, message);if (message == "exit") break;// 發送數據send(clientSocket, message.c_str(), message.size(), 0);// 接收回顯int bytesReceived = recv(clientSocket, buffer, sizeof(buffer), 0);if (bytesReceived > 0) {std::cout << "Server echoed: " << std::string(buffer, bytesReceived) << std::endl;}} while (true);// 5. 清理資源closesocket(clientSocket);WSACleanup();return 0;
}

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四、關鍵代碼解析

1. socket() 參數說明

• AF_INET：IPv4地址族。
• SOCK_STREAM：面向流的傳輸協議（TCP）。
• IPPROTO_TCP：明確指定TCP協議（可填0自動選擇）。

2. bind() 的地址設置

• INADDR_ANY：若服務器需要監聽所有網卡，可改為：

serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);  // 監聽所有網卡

3. listen() 的待處理隊列

• SOMAXCONN：系統允許的最大掛起連接數（Windows默認為200）。

4. accept() 的阻塞特性

• 若無客戶端連接，accept()會一直阻塞，直到新連接到達。

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五、運行與測試

1. 客戶端輸入/輸出

2. 服務器端輸出