Inheritance and method overloading

Question

Why C++ compiler gives this error? Why i can access lol() from B, but can not access rofl() [without parameters]. Where is the catch?

class A
{
public:
   void lol(void) {}
   void rofl(void) { return rofl(0);}
   virtual void rofl(int x) {}
};

class B : public A
{
public:
   virtual void rofl(int x) {}
};

int _tmain(int argc, _TCHAR* argv[])
{
    A a;
   a.lol();
   a.rofl(1);
   a.rofl();

   B  b;
   b.lol();
   b.rofl(1);    
   b.rofl(); //ERROR -> B::rofl function does not take 0 arguments


   return 0;
}

xtofl · Accepted Answer · 2010-06-04 12:22:41Z

34

The B::rofl(int) 'hides' the A::rofl(). In order to have A's rofl overloads, you should declare B to be using A::rofl;.

class B : public A {
public: 
    using A::rofl;
    ...
};

This is a wise move of C++: it warns you that you probably also need to override the A::rofl() method in B. Either you do that, or you explicitly declare that you use A's other overloads.

answered Jun 4, 2010 at 12:22

xtofl

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5 Comments

0xDEAD BEEF Over a year ago

yep, but A::rofl() is not virtual. Thats the idea - rofl() allways calls virtual rofl(0).

xtofl Over a year ago

@0xDEAD BEEF: in that case, you intend to use it, so make that clear to the compiler by saying using A::rofl;.

xtofl Over a year ago

@0xDEAD BEEF: btw, you are creating a 'non-virtual interface' this way; you probably want your A::rofl(int) to be pure virtual, and protected.

0xDEAD BEEF Over a year ago

No. I want to crate pure virtual Read(buffer, size, timeout), and wrapper (override) Read(buffer, size) { Read(buffer, size, 0);} BTW - using keyword works great!

Matthieu M. Over a year ago

@xtofl with such method names, the question was cut out for you :p

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