Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!rocket!dove
From: dove@rocket.UUCP (Webster Dove)
Newsgroups: comp.lang.c++
Subject: abstract class constructor pitfall
Message-ID: <DOVE.89Jun6233905@rocket.UUCP>
Date: 6 Jun 89 14:39:05 GMT
Sender: news@rocket.UUCP
Distribution: comp
Organization: Sanders Advanced Technology Dept.
Lines: 30
Posting-Front-End: GNU Emacs 18.44.4 of Tue May 12 1987 on rocket (berkeley-unix)

The constructor a::a() is booby trapped.  Since the virtual mechanism
does not work during construction, the attempted call to foo() is
undefined.  g++-1.35.0 creates an a.out that IOtraps on this.

// -*- C++ -*-

#include <stream.h>

class a
{
public: 
  virtual void foo() = 0;
  a() { foo(); }
};

class c_a : a
{
public:
  virtual void foo() { cout << "c_a\n"; }
};

main()
{
  c_a y;
}
--
		Dr. Webster Dove
		Computing Systems and Architectures
		Advanced Signal Processing Engineering (ASPEN) Dept.
		Sanders Associates (a Lockheed Company)