TITLE: Possible to call undefined pure virtual functions


[ Example adapted from "C++ Gotchas", tutorial by Tom Cargill,
  p. 24 ]


Given the following program:

	#include <stdio.h>

	class Base {
	  public:
	    Base () { g(); }
	    void g() { f(); }
	    virtual void f () = 0;
	};

	class D : public Base {
	  public:
	    virtual void f() { printf ("D::f\n"); }
	};

	int main ()
	{
	    D d;
	    return 0;
	}

could possibly result in a crash. The reason is that at the time Base
is being constructed, D does not yet exist. This is the reason that
calling virtual functions from constructors will not call overridden
versions of virtual methods for derived classes.

Note that if f() was called directly from the Base constructor, the
compiler would have caught the error.