Virtual function invocation from constructor [duplicate]

Question

Maybe I am wrong, but this seems to be a very basic question. Suddenly my inheritance chain stopped working. Writing a small basic test application proved that it was me that was wrong (so I can't blame the compiler).

I have a base class, with the default behavior in a virtual function. A child class derives from that and changes the behavior.

#include <iostream>

class Base
{
public:
    Base() { print(); }
    ~Base() {}

protected:
    virtual void print() { std::cout << "base\n"; }
};

class Child : public Base
{
public:
    Child() {}
    ~Child() {}

protected:
    virtual void print() { std::cout << "child\n"; }
};

int main()
{
    Base b;
    Child c;
}

This prints:

base
base

When a Child instance is created, why is Base::print() called? I thought that by using the virtual keyword, the function can be replaced for the derived class.

At what point did I get myself confused?

Answer 1

You are calling a virtual method in the constructor, which is not going to work, as the child class isn't fully initialized yet.

See also this StackOverflow question.