回调函数简析

#ifndef CAR_H
#define CAR_H
#include "engine.h"
#include <iostream>
#include <stdio.h>
#include <string>
#include <functional>
using namespace std;
class Car
{
public:
Car(Engine *engine);
~Car();
public:
void show_info();
public:
Engine *m_Engine;
};
#endif // CAR_H

#include "car.h"
Car::Car(Engine *engine)
{
    m_Engine = engine;
    m_Engine->m_f = std::bind(&Car::show_info, this);  //绑定widget中的回调
}
Car::~Car()
{
    if (m_Engine != 0)
    {
        delete m_Engine;
            m_Engine = 0;
    }
}
void Car::show_info()
{
    std::cout << "this is my first car." << std::endl;
}

#ifndef ENGINE_H
#define ENGINE_H
#include "engine.h"
#include <iostream>
#include <stdio.h>
#include <string>
#include <functional>
using namespace std;
typedef std::function<void()> Func;  //定义函数指针 返回值为void，参数为int型
class Engine
{
public:
    Engine();
public:
    Func m_f;
};
#endif // ENGINE_H

#include "engine.h"
Engine::Engine(){}

Engine *engine = NULL;
Car *car = NULL;
engine  = new Engine();
car = new Car(engine);

engine->m_f();

本质：将函数指针作为函数参数传递。类和类的关系是关联，一个类作为另一个类的成员。