Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!lll-tis!ames!ptsfa!pacbell!att-ih!occrsh!erc3ba!rsc
From: rsc@erc3ba.UUCP (Rich Chomiczewski, AT&T - ERC, Princeton NJ)
Newsgroups: comp.lang.c++
Subject: Following code bombs (possible assignment/initialization problem)?
Message-ID: <400@erc3ba.UUCP>
Date: 4 Mar 88 18:21:42 GMT
Organization: AT&T ERC, Princeton NJ
Lines: 54
Keywords: c++ X(X&) operator=(X&)


The following program blows the stack:

// --------------------- Cut Here --------------------
#include <stream.h>

class Point {
	int xc, yc;	// x-y coordinates
public:
	Point(int x =0, int y =0)	{ xc = x; yc = y; }
	int x()				{ return xc; }
	int y()				{ return yc; }
	Point operator+(Point p)	{ return Point(xc+p.xc, yc+p.yc); }
};
ostream& operator<<(ostream& oo, Point p)
{
	return oo << "(" << p.x() << "," << p.y() << ")";
}

class Position {
	Point off;	// offset is relative to (possibly null) ``to''.
	Position *to;
public:
	Position()			{ off = Point(0,0); to = 0; }
	Position(Point p)		{ off = p; to = 0; }
	Position(Point p, Position pos)	{ off = p; to = &pos; }
	Point position()		{ return (to) ? off+to->position() : off; }
};
ostream& operator<<(ostream& oo, Position p)
{
	return oo << p.position();
}

main()
{
	Position a = Position(Point(1,1));
	Position b = Position(Point(5,5), a);
	Position c = Position(Point(10,10), b);

	cerr << a;
	cerr << b;
	cerr << c;
}
// --------------------- Cut Here --------------------

One of the more difficult aspects of programming in c++ for me is
the correct handling of assignment and initialization of classes (which
I suspect is the root of the problem here).

So, given the above declaration of class Position what is the "correct"
definition of the member functions ``Position::Position(Position&)'' and 
``Position::operator=(Position&)''?

Thanks,
Rich Chomiczewski (ihnp4!erc3ba!rsc)