【C++】传递‘类非静态成员函数’用作回调函数

在C语言中，传递函数指针是非常常见的操作。

在C++语言中，使用C语言一致的方法传递全局函数指针，或者传递静态函数指针也很常见。

不过如果遇到想传递非静态成员函数时，可以参考以下示例代码。

#ifndef _WORKER_HPP_
#define _WORKER_HPP_#include <iostream>
#include <unistd.h>
#include <functional>
#include <chrono>
#include <iomanip>
#include <sstream>class Worker {
public:// 设置回调函数void registerCallback(std::function<void(int, std::string, long)> cb) {this->mCallback = cb;}void startWork() {using namespace std::literals;const std::chrono::time_point<std::chrono::system_clock> now = std::chrono::system_clock::now();const std::time_t t_c = std::chrono::system_clock::to_time_t(now);int i = 1008;std::stringstream ss;ss << std::put_time(std::localtime(&t_c), "%F %T");std::string s = ss.str();long l = __cplusplus;mCallback(i, s, l);}private:std::function<void(int, std::string, long)> mCallback;};#endif

参考Manager内的work函数，列出了几种写法。

#ifndef _MANAGER_HPP_
#define _MANAGER_HPP_#include <functional>
#include <string>
#include <iostream>#include "worker.hpp"class Manager {
public:Manager(): mI(-1), mS("coco"), mL(-1L) {}virtual ~Manager() = default;public:void work() {using namespace std::placeholders;// 设置回调函数， 使用lambdaworker.registerCallback([this](int&& i, std::string&& s, long&& l) -> void {this->onMsgCallback(i, s, l);});// 设置回调函数，使用bind，搭配mem_fnauto ptr = std::mem_fn(&Manager::onMsgCallback);worker.registerCallback(std::bind(ptr, this, _1, _2, _3));// 不搭配mem_fnworker.registerCallback(std::bind(&Manager::onMsgCallback, this, _1, _2, _3));worker.startWork();}void print() {std::cout << __FUNCTION__ << " mI is " << mI << ", mS is " << mS << ", mL is " << mL << std::endl;}private:void onMsgCallback(int i, std::string s, long l) {std::cout << __FUNCTION__ << " i is " << i << ", s is " << s << ", l is " << l << std::endl;this->mI = i;this->mS = s;this->mL = l;}private:int mI;std::string mS;long mL;Worker worker;
};#endif

main示例：

int main()
{// 演示将非静态成员函数设置为回调函数{Manager manager;manager.print();manager.work();manager.print();}return 0;
}

 输出参考：

print mI is -1, mS is coco, mL is -1
onMsgCallback i is 1009, s is 2023-11-18 20:22:34, l is 201402
print mI is 1009, mS is 2023-11-18 20:22:34, mL is 201402