I am having some troubles with member function pointers. How do I fix this, and why doesn't this work? The issue is inside main()
... or so I am guessing!
#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;
}
CodePudding user response:
The type of vtable_ptr
is void (Base::**)()
while the type of base->vtable_ptr[0]
is void (Base::*)()
. The syntax that you're using for the call is incorrect.
How do I fix this
The correct syntax of using the pointer to member function void (Base::*)()
in your example would be as shown below:
(base->*(base->vtable_ptr[0]))();
Note that there was no need for the Derived
class in the minimal reproducible example that you've provided.