Path: utzoo!attcan!uunet!mcvax!hp4nl!kunivv1!atcmpe!leo
From: leo@atcmp.nl (Leo  Willems)
Newsgroups: comp.lang.c++
Subject: istream conversion operator
Keywords: istream conversion operator
Message-ID: <522@atcmpe.atcmp.nl>
Date: 24 May 89 18:38:21 GMT
Organization: AT Computing, Nijmegen, The Netherlands
Lines: 29

In: 
	int i;
	while ( cin >> i) 
		//...

the expression  ``cin >> i'' gives as result an istream&.
That's the part I understand.

This istream& (which represents an istream object) is converted
using  ``operator istream*() { return _eof < state ? 0 : this; }''
to give a value which can be used in a while expression

My question is: Why does this conversion take  place? There is no
assignment involved (i.e. to a void*) from which the type system can decide
which conversion is appropriate.

The only explanation I can give is that class istream has only one 
conversion operator so there isn't much choise.

	1) if my explanation is incorrect, then where did I go wrong
	2) correct or not: the returning ``this'' from the  conversion
	   operator is a pointer, not a reference. Does is get converted
	   somehow to a reference?

Leo Willems				Internet: leo@atcmp.nl
AT Computing				UUCP:     mcvax!hp4nl!kunivv1!atcmpe!leo
P. O. Box 1428				
6501 BK  Nijmegen
The Netherlands