How do C++ functions implement network routing in network programming?

In network programming, C functions can implement routing by using sockets. First, sockets are created using the socket() function, specifying the domain, type, and protocol. Then, use the connect() and bind() functions to connect the local socket to the target host and bind it to a specific IP address and port number respectively. Through these functions, the routing of data packets from the source host to the destination host can be achieved.

Routing implementation of C function in network programming

In network programming, routing refers to routing data packets from the source host passed to the target host. Routing can be implemented in C by using sockets.

sockets

Sockets are network interfaces through which applications communicate with other applications over the network. In C, you can use the following function to create sockets:

int socket(int domain, int type, int protocol);

where:

• domain specifies the socket type, for example AF_INET represents IPv4 , AF_INET6 represents IPv6.
• type Specifies the communication method of the socket, for example, SOCK_STREAM represents TCP streaming connection, SOCK_DGRAM represents UDP datagram.
• protocol Specifies the network protocol used, usually 0, indicating that it is selected by the system.

Routing

After creating sockets, you can use the following function to implement routing:

int connect(int sockfd, const sockaddr *addr, socklen_t addrlen);
int bind(int sockfd, const sockaddr *addr, socklen_t addrlen);

Among them:

• sockfd is the socket descriptor.
• addr is the sockaddr structure, containing the IP address and port number of the target host.
• addrlen is the length of the sockaddr structure.

connect() The function is used to establish a TCP connection and connect the local socket to the target host (Note: UDP datagrams do not require a connection). bind() The function is used to bind a local socket to a specific IP address and port number.

Practical case

The following is a simple C program that demonstrates how to use sockets and the above functions to implement routing:

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

int main() {
  // 创建一个 TCP socket
  int sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd == -1) {
    std::cerr << "无法创建 socket" << std::endl;
    return 1;
  }

  // 绑定 socket 到本地 IP 地址和端口号
  sockaddr_in addr;
  addr.sin_family = AF_INET;
  addr.sin_addr.s_addr = INADDR_ANY;
  addr.sin_port = htons(8080); // 端口号 8080
  if (bind(sockfd, (sockaddr *)&addr, sizeof(addr)) == -1) {
    std::cerr << "无法绑定 socket" << std::endl;
    return 1;
  }

  // 侦听连接请求
  if (listen(sockfd, 10) == -1) { // 队列中最多可以有 10 个未处理的连接
    std::cerr << "无法侦听连接请求" << std::endl;
    return 1;
  }

  // 接受连接请求
  sockaddr_in clientAddr;
  socklen_t clientAddrLen = sizeof(clientAddr);
  int clientSockfd = accept(sockfd, (sockaddr *)&clientAddr, &clientAddrLen);
  if (clientSockfd == -1) {
    std::cerr << "无法接受连接请求" << std::endl;
    return 1;
  }

  // 处理客户端请求
  char buffer[1024];
  int len = read(clientSockfd, buffer, sizeof(buffer));
  if (len > 0) {
    std::cout << "收到来自客户端的数据：" << buffer << std::endl;
  }

  // 关闭连接
  close(clientSockfd);
  close(sockfd);

  return 0;
}

In this case, The program creates a TCP socket and binds it to the local IP address and port number 8080. It then listens for connection requests and accepts the first one. Finally, it reads the data sent by the client and closes the connection.

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