7

I cant call protected function in my base class. Why? It looks something like this:

class B : B2
{
public:
  virtual f1(B*)=0;
protected:
  virtual f2(B*) { codehere(); }
}
class D : public B
{
public:
  virtual f1(B*b) { return f2(b); }
protected:
  virtual f2(B*b) { return b->f2(this); }
}

In msvc I get the error error C2248: 'name::class::f2' : cannot access protected member declared in class 'name::class'

In gcc I get error: 'virtual int name::class::f2()' is protected.

Why is that? I thought the point of protected members is for derived classes to call.

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2
  • At least add code that will compile and generate the errors you want us to fix. The code above has so many other syntax errors that solving your problem becomes irrelavant.
    – Loki Astari
    Commented Jan 25, 2009 at 15:58
  • i agree with martin. if you want us to help you, invest some time in making your code c++ (not omitting return types, semicolons and other stuff)
    – Johannes Schaub - litb
    Commented Jan 25, 2009 at 16:29

1 Answer 1

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15

Protected member functions can only be called inside the base class or in its derived class. You cannot call them outside your class. Outside calling means calling a member function of a class-typed variable.

So

virtual f1(B*b) { return f2(b); }

is ok, because f2 operates on the class itself. (called inside)

But

virtual f2(B*b) { return b->f2(this); }

won't compile, because f2 operates on b not the class D itself. (called outside) It's illegal.

To fix it B::f2 should be public.

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2
  • Question, is there any way around this, I come from the managed world, where this is allowed and I find it very useful, I don't really just wanna make these private things internal but if there's no way around it, I guess I have to. Is it possible to make the class a friend of itself?
    – John Leidegren
    Commented Jan 19, 2012 at 7:50
  • John, either make f2 public or declare D to be a friend of B. I'm aware of no other way.
    – Jeff Wofford
    Commented Jan 21, 2012 at 15:54