c++ - 回调lambda到std::function 0xCCCCCCCC

正确一点：

我有一堂课（按钮）

我想让该按钮执行另一个类（游戏）拥有的非静态成员函数

public:
template<class Class>
explicit Button(void (Class::*func)(), Class* T) {
//(T->*func)(); // OK

m_PressFunction = [&](){(T->*func)()};
m_PressFunction(); // OK
}
private:
std::function<void()> m_PressFunction{nullptr}; //STAYS NULLPTR?

问题是：一旦保留作用域，m_PressFunction就会变为nullptr。

如何正确存储？

UPD

Minimal, Complete, and Verifiable example，如@aschepler所问：

#include <functional>
#include <iostream>

class Button {
public:
    explicit Button() {};
    explicit Button(const Button& other) { m_PressFunction = other.m_PressFunction; };
    explicit Button(Button&& other) { m_PressFunction = other.m_PressFunction; };
    Button& Button::operator=(const Button& other) { m_PressFunction = other.m_PressFunction; return *this; };
    Button& operator=(Button&& other) { m_PressFunction = other.m_PressFunction; return *this; };
    ~Button() {};

    template<class Class>
    explicit Button(void (Class::*func)(), Class& T) {
    m_PressFunction = [&]() {(T.*func)(); };
    m_PressFunction(); // OK
    }

    void runPressFunction() { if (m_PressFunction != nullptr) { m_PressFunction(); } else std::cout << "Tried to run nullptr m_PressFunction. IT DOES NOT WORK\n"; };
private:
    std::function<void()> m_PressFunction{ nullptr }; //STAYS NULLPTR?

};

class Game {
public:
    Game::Game() { m_Button = Button(&Game::PressFunction, *this); };

    void runButtonFunction() { m_Button.runPressFunction(); };
private:
    void PressFunction() { std::cout << "Game::PressFunction() called. IT WORKS\n"; };
    Button m_Button;
};

int main() {
    Game game;
    game.runButtonFunction();

    std::cin.get();
}

好吧，它不再是null（我很遗憾忘记将m_PressFunction设置为5的规则），但是它仍然无法正常工作。有什么提示吗？

最佳答案

终于解决了。

template<class Class>
        explicit Button(void (Class::*func)(), Class* const T) {
            m_PressFunction = [T, func]() {(T->*func)(); };
        }