libstdc++/4442: bad fstream behavior <synopsis of the problem (one line)>

[Phil Edwards]

The following reply was made to PR libstdc++/4442; it has been noted by GNATS.

From: Phil Edwards <pedwards@disaster.jaj.com>
To: andrew@werdna.com
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: libstdc++/4442: bad fstream behavior 	<synopsis of the problem (one line)>
Date: Tue, 2 Oct 2001 16:38:04 -0400

 On Tue, Oct 02, 2001 at 02:47:54PM -0400, Andrew Haydn Grant wrote:
 > >Description:
 > fstreams handle certain odd situations differently than they used to,
 > causing old code to break.
 
 The behavior you're seeing is, unfortunately, unspecified by the standard.
 Even more unfortunately, the currently recommended resolution is to
 maintain this behavior.  For more, see the C++ homepage linked to from
 the GCC "Readings" list, and look for LWG defect report 22.
 
 (I /must/ remember to add this to the FAQ...)
 
 
 > void fail()
 > {
 >   fstream f;
 >   f.close();
 >   f.open("hello.txt", ios::in);
 >   char buffer[2048];
 >   f.getline(buffer, 2048);
 >   cout << "FILE CONTENTS" << buffer << "FILE CONTENTS\n";
 > }
 > 
 > The fail() function does not read "hello.txt".  If you remove the initial
 > f.close() call, it reads "hello.txt" without difficulty.
 
 You can place a call to f.clear() between the close() and the open(),
 then it will work.  Also note that this will /not/ display the entire
 contents of hello.txt, only the first line.
 
 
 > void failWrite()
 > {
 >   fstream f;
 >   f.open("/tmp/empire/simout.txt", ios::in);
 >   f.close();
 >   f.open("/tmp/empire/simout.txt", ios::out);
 >   f << "It went out!!!\n";
 > }
 
 Likewise, a call to clear() between open() and close() will make this work
 as you (and the rest of us) expect it to.
 
 Phil
 
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