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.