Usage of C++ function default parameters and variable parameters in asynchronous programming

In asynchronous programming, the default parameters and variable parameters features of C functions can simplify callback functions: default parameters allow optional parameters to be omitted, reducing the complexity of writing and using callback functions. Variable parameters allow any number of parameters to be passed to the function, making it easy to pass dynamic parameter lists.

Usage of C function default parameters and variable parameters in asynchronous programming

In an asynchronous programming system, the code usually involves Callback. When the operation is completed, the callback function is executed, which can receive various parameters, including the result of the operation. However, writing and using callback functions can be complex and error-prone.

The default parameters and variadic features of C functions allow us to simplify callback functions and reduce the possibility of errors.

Default parameters

The default parameters of a function allow us to omit optional parameters. This is useful in the context of callback functions, where some parameters may be optional.

For example, consider the following callback function:

void callback(int result, const std::string& message = "") {
  // ...
}

With the default parameters, we can omit the optional message parameter:

callback(42);

Can Variable parameters

The variable parameters feature of a function allows us to pass any number of parameters to the function. This is useful for functions such as operator<< in std::cout that require arguments of different types.

In asynchronous programming, variable parameters are also useful when we need to pass a dynamic parameter list to the callback function.

Consider the following callback function:

void callback(int result, std::vector<int>& values) {
  // ...
}

Using variable parameters, we can pass any number of values ​​​​to the callback function:

std::vector<int> values = {1, 2, 3};
callback(42, values);

Practical case

The following is a practical case that demonstrates how to use default parameters and variadic parameters to simplify asynchronous programming:

#include <iostream>
#include <future>
#include <vector>

using namespace std;

// 异步函数
future<int> async_sum(std::vector<int>& values) {
  return async([=]() {
    int sum = 0;
    for (int value : values) {
      sum += value;
    }
    return sum;
  });
}

// 回调函数
void callback(int result, const std::string& message = "") {
  cout << "结果: " << result << endl;
  if (!message.empty()) {
    cout << "消息: " << message << endl;
  }
}

int main() {
  std::vector<int> values = {1, 2, 3};
  auto future = async_sum(values);

  // 使用默认参数省略可选的 message 参数
  future.then(callback);

  // 使用可变参数传递动态参数列表
  future.then(callback, "完成");

  return 0;
}

In this example, the async_sum function uses variadic parameters to accept any number of values ​​to be added. Then use std::async to start the asynchronous operation. callback The callback function uses default arguments to omit the optional message argument, and variadic arguments to accept a dynamic argument list.

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