How to implement asynchronous programming with C++ functions?

Summary: Asynchronous programming in C allows multitasking without waiting for time-consuming operations. Use function pointers to create pointers to functions. The callback function is called when the asynchronous operation completes. Libraries such as boost::asio provide support for asynchronous programming. The practical case demonstrates how to use function pointers and boost::asio to implement asynchronous network requests.

Use C functions to implement asynchronous programming

Introduction

Asynchronous programming is a A programming paradigm that allows a program to perform other tasks while waiting for time-consuming operations (such as network requests) to complete. In this process, the callback function will be called after the operation is completed without the program explicitly waiting. In C, asynchronous programming can be implemented using function pointers and related libraries.

Function pointer

The function pointer in C is a pointer to a function. We can create a function pointer from the name of the function like this:

int add(int a, int b) { return a + b; }

using AddFunction = int(*)(int, int);
AddFunction addPtr = &add;

addPtr is now a function pointer pointing to the add function.

Callback function

The callback function is a function that is called when certain events occur. When an asynchronous operation completes, the system calls the corresponding callback function. For example, the following function will be called when the network request is completed:

void networkCallback(const std::string& data) {
  // 使用 data 进行处理
}

Asynchronous libraries

There are many libraries in C that support asynchronous programming. One popular choice is boost::asio. This library provides many classes and functions for creating and managing asynchronous operations.

Practical Case

Let us create a simple example to demonstrate how to use function pointers and boost::asio to implement asynchronous network requests:

#include <boost/asio.hpp>
#include <iostream>

using namespace boost::asio;

// 回调函数
void networkCallback(const boost::system::error_code& error,
                    boost::array<char, 1024> data) {
  if (!error) {
    std::cout << data.data() << std::endl;
  } else {
    std::cout << "Error: " << error.message() << std::endl;
  }
}

int main() {
  using namespace std::placeholders;

  // 创建 IO 服务
  io_service service;

  // 创建 IP 协议套接字
  ip::tcp::socket socket(service);

  // 连接到服务器
  socket.connect(
      ip::tcp::endpoint(ip::address::from_string("127.0.0.1"), 8080));

  // 发送请求
  std::string request = "GET / HTTP/1.1\r\n\r\n";
  std::async_write(socket, buffer(request), networkCallback, _1);

  service.run();

  return 0;
}

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