Question

I have a base class A that I am extending with X. Inside of A there is another class, B. It seems like the virtual method is not being defined, but I don’t understand why?

class A {
 public:
  class B {public: bool value;};

  A() {}
  B b_;
  void DoStuff(B& b);
 private:
  virtual void DoStuffImpl(B& b) = 0;
};

class X : public A {
 public:
  X() {}
  void Trigger();
 private:
  virtual void DoStuffImpl(B& b);
};

void A::DoStuff(B& b) {
     DoStuffImpl(b);
}

void X::Trigger() {
    DoStuff(b_);
}
void X::DoStuffImpl(B& b) {
    b.value = true;
}

int main(){
    X x;
    x.Trigger();
    return x.b_.value;
}

P.S. This came up because I am having a different problem with my code, but I couldn’t even make this toy example work, so now I have this making me curious….

Here is a link to the above code, which is compiling and failing to run: http://ideone.com/mBJ1Kg

Answer 1

It runs fine. ideone reports a “runtime error” with an exit code of 1 because you return 1 from main. A non-zero return code is conventionally considered to be a failure.

If you comment out your return x.b_.value line and replace it with return 0 then everything’s fine.

You could have put some std::cout lines in there to see what’s going on, and see that the program works! 😀