类成员函数变量指向另一个类函数成员

Question

can you please explain me why this code shows nothing except for the last std::cout line in main()? Checked through similar threads on stackoverflow.com, was not able to connect them to mine, is this pointing legal at all? I try to set a function pointer of a class to another class function:

#include <iostream>

class container;

class one {
public:
one() 
    { 
        eventsHandler = NULL; 
    };
~one() {}; 

void (container::*eventsHandler)();
};

class container {
public:
    container() 
    { 
        zone = new one;
        zone->eventsHandler = &container::events;
    };
    ~container()
    { 
        delete zone; 
    };

    one *zone;
    void events()
    {
        std::cout << "event handler is on..." << std::endl;
    };
};

int main()
{
    container *test = new container;
    test->zone->eventsHandler;

    std::cout << "just checker..." << std::endl;
    delete test;

    system("pause");
};

Answer 1

You should use operator->* for calling the member function pointer, and assign test as the object which will be called on,

(test->*test->zone->eventsHandler)();

or more clear,

(test->*(test->zone->eventsHandler))();

LIVE

Answer 2

你必须在第38行实际调用函数指针，如下所示：

(test->*test->zone->eventsHandler)();

Answer 3

You need to provide an object to call a pointer to memeber function:

container *test = new container;
(test->*test->zone->eventsHandler)();

Here, test is the object, test->zone->eventsHandler is the pointer to member function that you have saved, and operator->* joins them.

So, it is very much like any other member function; however, you can switch which objects to call a member on:

container *first = new container;
container *second = new container;
(first->*second->zone->eventsHandler)();
// both pointers point to the same function
std::cout << (first->zone->eventsHandler == second->zone->eventsHandler) << std::endl;