Newsgroups: comp.lang.c++
Path: utzoo!censor!geac!alias!rae
From: rae@alias.com (Reid Ellis)
Subject: Re: istream problem
Message-ID: <1991May25.174532.15632@alias.com>
Sender: news@alias.com (0000-news(0000))
Organization: Alias Research, Inc., Toronto ON Canada
References: <1991May23.181402.7912@milton.u.washington.edu>
Distribution: usa
Date: Sat, 25 May 1991 17:45:32 GMT

Michael Kenney <kenney@milton.u.washington.edu> writes:
|    func(istream &in)
|    {
|	.
|	.
|	.
|	while(in.get(c))
|	{
|	    // Do something
|	}
|
|	in.seekg(0, ios::beg);
|
|	// This loop FAILS
|	while(in.get(c))
|	{
|	    // Do something else
|	}
|   }
|
|The problem is, the second while loop never iterates, in.get() returns
|0.  I used in.tellg() to insure that the stream is repositioned, and it
|is.  Am I missing something obvious?

Well, you *are* missing something, but no, it isn't obvious [which is
why I'm posting].  I discovered this when I derived a couple of
classes from fstream and streambuf.

The problem is that ios [from which both istream and ostream are
derived] maintains a state within itself, WHICH IS NOT RESET WHEN YOU
'REWIND' THE STREAM.  It took me a few hours to figure this one out.
So, all you have to do is reset the error state of the stream, by
saying "in.clear();" after you hit EOF.  I don't think it matters if
you call clear() before or after the seekg().

Hope this helps other people bitten by the same thing.  I'm still of
two minds about whether istream::seekg() [and ostream::seekp() for
that matter] should reset the ios::eofbit bit of the error state..

					Reid
--
Reid Ellis
rae@utcs.toronto.edu        ||               rae@alias.com
CDA0610@applelink.apple.com ||      +1 416 362 9181 [work]