From:	"Peter Lewerin" <peter DOT lewerin AT krax DOT pp DOT se>
Newsgroups:	comp.os.msdos.djgpp
Subject:	fstream open mode interpretation
Date:	18 May 1997 11:46:55 GMT
Organization:	-
Lines:	25
Message-ID:	<01bc6381$26125d40$LocalHost@peterlew>
NNTP-Posting-Host:	dialup156-2-10.swipnet.se
NNTP-Posting-User:	s-36170
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

I'm trying to translate stdio file operations to fstream f.o. in an
introductory text for beginning programmers.  The problem is with file open
mode "r+".  According to the draft C++ standard
(<http://www.cygnus.com/misc/wp/draft/lib-iostreams.html#lib.filebuf.members
>), the corresponding flags are ios::in|ios::out; the file should not be
truncated unless ios::trunc is set.

However, DJGPP (2.01, gcc version 2.7.2.1) always truncates the supplied
file, regardless of ios::trunc setting.  (This seems to be standard
behaviour for older C++ compilers; TC++ 3.0 does it too.)

Is there any -simple- workaround for this?

 * I suppose I could open a stdio stream and use the file descriptor as a
parameter to the fstream ctor, but, hey...
 * ios::app is no use, either; I'm trying to show the effects of reading a
random byte, reseeking and reinserting it randomly.
 * I don't want to patch the sources, even if I could figure out how,
because I want those beginning programmers to be able to use DJGPP out of
the box on their own systems.

TIA.

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