访问指向成员函数的指针数组的元素

Question

我在使用成员函数指针时遇到了一些问题。我该如何解决这个问题，为什么它不起作用？问题出在 main() 内……我猜大概是这样！

#include <iostream>
#include <functional>

template<typename T>
using FnctPtr = void(T::*)(); // pointer to member function returning void

class Base {    
public:
    Base() : vtable_ptr{ &virtual_table[0] } {}
    void foo() {
        std::cout << "Base";
    }
    void x() { 
        std::cout << "X";
    }

 
private:
    // array of pointer to member function returning void
    inline static FnctPtr<Base> virtual_table[2] = { &Base::foo, &Base::x };

public:
    FnctPtr<Base>* vtable_ptr;
};

class Derived : public Base {
public:
    Derived() {
        vtable_ptr = reinterpret_cast<FnctPtr<Base>*>(&virtual_table[0]);
    }
    void foo() /* override */ {
        std::cout << "Derived";
    }

public:
    inline static FnctPtr<Derived> virtual_table[2] = { &Derived::foo, &Base::x };
};

int main() {
    Base* base = new Base();
    base->vtable_ptr[0](); // Issue here
    delete base;
}

Answer 1

vtable_ptr的类型是void (Base::**)()，base->vtable_ptr[0]的类型是void (Base::*)()。您用于调用的语法不正确。

How do I fix this

在您的示例中使用 成员函数指针 void (Base::*)() 的正确语法如下所示：

(base->*(base->vtable_ptr[0]))();

请注意，在您提供的最小可重现示例中不需要 Derived class。

Working demo

访问指向成员函数的指针数组的元素

Accessing element of array of pointers to member functions

c++

pointers

function