How do C++ functions establish and close network connections in network programming?

In C network programming, establishing a network connection involves the following functions: socket(): Create a socket. connect(): Connect the socket to the remote host and port. To close a network connection, you need to use the close() function.

C function establishes and closes connections in network programming

In network programming, establishing and closing network connections is crucial important. C provides several functions for handling these operations.

Establishing a network connection

• socket(): Create a socket for network communication.
• connect(): Connect the socket to the remote host and port.

Code example: Establish TCP connection

#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 ...
}

Close network connection

• close (): Close a socket.

Code example: Close TCP connection

#include <sys/socket.h>

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

  // 关闭套接字
  close(socket_fd);
}

Practical case

Using the above function, you can easily Implement connection establishment and closing in network programming in C. For example, write a simple TCP client and server to demonstrate what these functions do.

Client code:

#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;
}

Server code:

#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;
}

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