Bagaimanakah fungsi C++ mewujudkan dan menutup sambungan rangkaian dalam pengaturcaraan rangkaian?

#include <sys/socket.h>
#include <netinet/in.h>

int main() {
  // 创建套接字
  int socket_fd = socket(AF_INET, SOCK_STREAM, 0);

  // 设置服务器地址信息
  struct sockaddr_in server_addr;
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(8080);
  server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

  // 连接到服务器
  connect(socket_fd, (struct sockaddr *) &server_addr, sizeof(server_addr));
  
  // ... 继续执行其他操作 ...
}

#include <sys/socket.h>

int main() {
  // ... 获取已连接的套接字 fd ...

  // 关闭套接字
  close(socket_fd);
}

#include <sys/socket.h>
#include <netinet/in.h>
#include <iostream>

int main() {
  // 创建套接字并连接到服务器
  int socket_fd = socket(AF_INET, SOCK_STREAM, 0);
  struct sockaddr_in server_addr;
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(8080);
  server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
  connect(socket_fd, (struct sockaddr *) &server_addr, sizeof(server_addr));

  // 发送数据到服务器
  std::string msg = "Hello from client!";
  send(socket_fd, msg.c_str(), msg.size(), 0);

  // 关闭连接
  close(socket_fd);

  return 0;
}

#include <sys/socket.h>
#include <netinet/in.h>
#include <iostream>

int main() {
  // 创建套接字并绑定到端口
  int socket_fd = socket(AF_INET, SOCK_STREAM, 0);
  struct sockaddr_in server_addr;
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(8080);
  server_addr.sin_addr.s_addr = INADDR_ANY;
  bind(socket_fd, (struct sockaddr *) &server_addr, sizeof(server_addr));

  // 监听连接
  listen(socket_fd, 5);

  // 接受连接
  int client_socket_fd = accept(socket_fd, NULL, NULL);

  // 从客户端接收数据
  char buffer[256];
  recv(client_socket_fd, buffer, sizeof(buffer), 0);
  std::cout << "Received from client: " << buffer << std::endl;

  // 发送响应到客户端
  std::string msg = "Hello from server!";
  send(client_socket_fd, msg.c_str(), msg.size(), 0);

  // 关闭连接
  close(client_socket_fd);
  close(socket_fd);

  return 0;
}