Can I override a non-virtual function in C++?

Question

I want to know if I can override a non-virtual function in C++. I found this problem when playing with the C++ override keyword. I have the code as follows :

class A
{
public:
    void say()
    {
        cout << "From A\n";
    }
};
class B : public A {
public:
    void say()
        override
    {
        cout << "From B\n";
    }
};

But when I execute the code, Visual Studio displays the following error:

'B::say': method with override specifier 'override' did not override any base class methods

But when I use the virtual keyword in class A, the error is gone and the code runs perfectly.

Answer 1

You do not override say in B

from C++ override specifier :

In a member function declaration or definition, override ensures that the function is virtual and is overriding a virtual function from a base class. The program is ill-formed (a compile-time error is generated) if this is not true.

Look at that example :

#include <iostream>

class A
{
  public:
    void say()
    {
        std::cout << "From A\n";
    }
};

class B : public A {
  public:
    void say()
        //override
    {
        std::cout << "From B\n";
    }
};

int main()
{
  A a;
  B b;
  
  a.say();
  b.say();
  ((A &) b).say();
}

Compilation and execution :

pi@raspberrypi:/tmp $ g++ c.cc
pi@raspberrypi:/tmp $ ./a.out
From A
From B
From A
pi@raspberrypi:/tmp $ 

Putting say virtual in A (so implicitely in B) ((A &) b).say(); prints From B because that time there is overriding