TCP/IP-——C++编程详解

1. TCP/IP 编程基本概念

• TCP（传输控制协议）：面向连接、可靠的传输层协议，保证数据顺序和完整性。
• IP（网际协议）：负责将数据包路由到目标地址。
• Socket（套接字）：网络通信的端点，通过IP和端口标识。

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2. 服务器端实现步骤

步骤 1：创建套接字

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

int main() {
    // 创建套接字
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (server_fd == -1) {
        std::cerr << "Socket creation failed\n";
        return -1;
    }

步骤 2：绑定套接字到地址和端口

    // 设置地址结构
    struct sockaddr_in address;
    address.sin_family = AF_INET;          // IPv4
    address.sin_addr.s_addr = INADDR_ANY;  // 绑定所有接口
    address.sin_port = htons(8080);        // 端口号（需转为网络字节序）

    // 绑定套接字
    if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
        std::cerr << "Bind failed\n";
        return -1;
    }

步骤 3：监听连接请求

    // 监听，队列长度设为5
    if (listen(server_fd, 5) < 0) {
        std::cerr << "Listen failed\n";
        return -1;
    }
    std::cout << "Server listening on port 8080...\n";

步骤 4：接受客户端连接

    // 接受连接
    int addrlen = sizeof(address);
    int new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen);
    if (new_socket < 0) {
        std::cerr << "Accept failed\n";
        return -1;
    }
    std::cout << "Client connected\n";

步骤 5：接收和发送数据

    // 接收数据
    char buffer[1024] = {0};
    int valread = read(new_socket, buffer, 1024);
    std::cout << "Received: " << buffer << std::endl;

    // 发送响应
    const char* response = "Hello from server";
    send(new_socket, response, strlen(response), 0);
    std::cout << "Response sent\n";

步骤 6：关闭套接字

    close(new_socket);
    close(server_fd);
    return 0;
}

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3. 客户端实现步骤

步骤 1：创建套接字

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

int main() {
    // 创建套接字
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == -1) {
        std::cerr << "Socket creation failed\n";
        return -1;
    }

步骤 2：设置服务器地址

    struct sockaddr_in serv_addr;
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(8080);  // 服务器端口

    // 将IP地址从字符串转为二进制格式
    if (inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
        std::cerr << "Invalid address\n";
        return -1;
    }

步骤 3：连接到服务器

    if (connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0) {
        std::cerr << "Connection failed\n";
        return -1;
    }
    std::cout << "Connected to server\n";

步骤 4：发送和接收数据

    // 发送数据
    const char* message = "Hello from client";
    send(sock, message, strlen(message), 0);
    std::cout << "Message sent\n";

    // 接收响应
    char buffer[1024] = {0};
    int valread = read(sock, buffer, 1024);
    std::cout << "Server response: " << buffer << std::endl;

步骤 5：关闭套接字

    close(sock);
    return 0;
}

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4. 关键函数和结构体

• socket(): 创建套接字。
• bind(): 绑定套接字到地址和端口。
• listen(): 进入监听状态。
• accept(): 接受客户端连接。
• connect(): 客户端连接到服务器。
• send()/recv() 或 write()/read(): 发送和接收数据。
• sockaddr_in: 存储地址信息的结构体（IPv4）。

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5. 注意事项

1. 错误处理：每次调用网络函数后检查返回值。
2. 字节序转换 ：
   • htons(): 主机字节序转网络字节序（端口）。
   • inet_pton(): 字符串IP转二进制。
3. 资源释放 ：使用 close() 关闭套接字。
4. 端口复用 ：通过 setsockopt() 设置 SO_REUSEADDR 选项。

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6. 完整示例代码

• 服务器端

  #include <iostream>
  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <unistd.h>
  #include <string.h>
  
  int main() {
      int server_fd, new_socket;
      struct sockaddr_in address;
      int addrlen = sizeof(address);
      char buffer[1024] = {0};
      const char* hello = "Hello from server";
  
      // 创建socket
      if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
          perror("socket failed");
          exit(EXIT_FAILURE);
      }
  
      // 绑定socket
      address.sin_family = AF_INET;
      address.sin_addr.s_addr = INADDR_ANY;
      address.sin_port = htons(8080);
  
      if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
          perror("bind failed");
          exit(EXIT_FAILURE);
      }
  
      // 监听socket
      if (listen(server_fd, 3) < 0) {
          perror("listen");
          exit(EXIT_FAILURE);
      }
  
      // 接受连接
      if ((new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen)) < 0) {
          perror("accept");
          exit(EXIT_FAILURE);
      }
  
      // 读取客户端发送的数据
      read(new_socket, buffer, 1024);
      std::cout << "Message from client: " << buffer << std::endl;
  
      // 向客户端发送数据
      send(new_socket, hello, strlen(hello), 0);
      std::cout << "Hello message sent\n";
  
      // 关闭socket
      close(new_socket);
      close(server_fd);
      return 0;
  }
  #include <iostream>
  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <unistd.h>
  #include <string.h>
  
  int main() {
      int server_fd, new_socket;
      struct sockaddr_in address;
      int addrlen = sizeof(address);
      char buffer[1024] = {0};
      const char* hello = "Hello from server";
  
      // 创建socket
      if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
          perror("socket failed");
          exit(EXIT_FAILURE);
      }
  
      // 绑定socket
      address.sin_family = AF_INET;
      address.sin_addr.s_addr = INADDR_ANY;
      address.sin_port = htons(8080);
  
      if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
          perror("bind failed");
          exit(EXIT_FAILURE);
      }
  
      // 监听socket
      if (listen(server_fd, 3) < 0) {
          perror("listen");
          exit(EXIT_FAILURE);
      }
  
      // 接受连接
      if ((new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen)) < 0) {
          perror("accept");
          exit(EXIT_FAILURE);
      }
  
      // 读取客户端发送的数据
      read(new_socket, buffer, 1024);
      std::cout << "Message from client: " << buffer << std::endl;
  
      // 向客户端发送数据
      send(new_socket, hello, strlen(hello), 0);
      std::cout << "Hello message sent\n";
  
      // 关闭socket
      close(new_socket);
      close(server_fd);
      return 0;
  }

• 客户端：

  #include <iostream>
  #include <sys/socket.h>
  #include <arpa/inet.h>
  #include <unistd.h>
  #include <string.h>
  
  int main() {
      int sock = 0;
      struct sockaddr_in serv_addr;
      char buffer[1024] = {0};
      const char* hello = "Hello from client";
  
      // 创建socket
      if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
          std::cerr << "Socket creation error" << std::endl;
          return -1;
      }
  
      // 设置服务器地址
      serv_addr.sin_family = AF_INET;
      serv_addr.sin_port = htons(8080);
  
      // 将IP地址从字符串转换为网络格式
      if (inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
          std::cerr << "Invalid address/Address not supported" << std::endl;
          return -1;
      }
  
      // 连接到服务器
      if (connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0) {
          std::cerr << "Connection Failed" << std::endl;
          return -1;
      }
  
      // 向服务器发送数据
      send(sock, hello, strlen(hello), 0);
      std::cout << "Hello message sent" << std::endl;
  
      // 读取服务器发送的数据
      read(sock, buffer, 1024);
      std::cout << "Message from server: " << buffer << std::endl;
  
      // 关闭socket
      close(sock);
      return 0;
  }

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编译运行：

# 编译服务器
g++ server.cpp -o server
# 编译客户端
g++ client.cpp -o client

# 启动服务器
./server
# 启动客户端（另起终端）
./client

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对于更复杂的场景（如多客户端并发），需结合多线程或异步I/O（如 select/epoll）进行扩展。