From: Joe Buck <jbuck@synopsys.com>
To: Olivier.Galibert@mines.u-nancy.fr (Olivier Galibert)
Cc: egcs@cygnus.com
Subject: Re: linux libio status
Date: Wed, 15 Oct 1997 11:12:00 -0000 [thread overview]
Message-ID: <199710151604.JAA22390@atrus.synopsys.com> (raw)
In-Reply-To: <19971015095211.03621@renaissance.loria.fr>
>
> On Tue, Oct 14, 1997 at 11:23:49PM -0700, Joe Buck wrote:
> > We need to silence these warnings. For the NULL, I suggest a global
> > s/NULL/0/ in the C++ iostreams headers. There is no reason to write
> > NULL, it is just a source of problems like this (*especially* since
> > we have changed C++ to be strict about void*).
>
> Don't use '0' but '0L'. This way you will be OK with NULL in stdargs
> when int=32b and pointer=64b.
And you'll be broken on platforms where sizeof(long) != sizeof(pointer),
or at least you would if it weren't for the fact that C++ requires
prototypes for all functions. Remember, we are talking about C++ here,
not C.
Stroustrup says (The C++ Programming Language, 3rd Edition, p. 88)
"Because of C++'s tighter type checking, the use of plain 0, rather than
any suggested NULL macro, leads to fewer problems. If you feel that you
must define NULL, use
const int NULL = 0;
..."
There is a similar discussion in the comp.lang.c++ FAQ.
In C++, there are always prototypes. Thus 0 or 0L makes no difference,
and in fact the "standard null pointer" is essentially 0 in C++. The
argument is coerced to the proper pointer. However, standard C++ does
not let you convert (void *) to (T *) without a cast, so defining NULL
as (void *)0 is completely broken in C++. It used to work in g++, but
that was an extension (furthermore this extension prevented g++ from
implementing the standard overloading rules correctly). Hence
The only exception is functions with ... in their spec. Here, neither 0
nor 0L will result in portable code. Your suggestion switches the
erroneous assumption that sizeof(T *) == sizeof(int) with another
erroneous assumption, that sizeof(T *) == sizeof(long). Worse, you leave
users with the idea that they can safely use NULL for any null pointer
type, even in variadic functions. Sorry, you can't do that in standard
C++. For variadic functions, users must declare any optional arguments
correctly, period.
Conclusion: we should deprecate the use of NULL in C++ code. If we
must define NULL for C++ code, it must be 0. Nothing else.
next prev parent reply other threads:[~1997-10-15 11:12 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-10-14 23:23 Joe Buck
1997-10-15 0:06 ` Richard Henderson
1997-10-15 0:52 ` Olivier Galibert
1997-10-15 8:25 ` [ECGS] " chip
1997-10-15 11:12 ` Joe Buck [this message]
1997-10-15 12:10 ` Olivier Galibert
1997-10-15 16:51 ` [ECGS] " chip
1997-10-15 20:16 ` Joe Buck
1997-10-15 20:16 ` Olivier Galibert
1997-10-16 12:53 ` Pal Engstad
1997-10-15 11:12 ` Peter Seebach
1997-10-15 20:16 ` Joe Buck
[not found] ` <199710151419.JAA20162.cygnus.egcs@monolith.solon.com>
1997-10-15 16:51 ` Jason Merrill
1997-10-15 20:16 ` Peter Seebach
1997-10-15 22:29 ` Jason Merrill
1997-10-16 8:31 ` Peter Seebach
1997-10-16 15:19 ` Jason Merrill
1997-10-16 12:53 ` Peter Seebach
1997-10-16 15:19 ` Paul Koning
[not found] <199710150623.XAA06491.cygnus.egcs@atrus.synopsys.com>
1997-10-15 2:10 ` Jason Merrill
1997-10-15 9:15 ` Joe Buck
1997-10-15 11:12 ` Per Bothner
1997-10-15 14:33 ` Joe Buck
1997-10-15 16:51 ` Per Bothner
[not found] ` <199710152351.QAA02138.cygnus.egcs@cygnus.com>
1997-10-16 1:51 ` Jason Merrill
1997-10-16 12:58 ` Alexandre Oliva
1997-10-16 12:58 ` Joe Buck
1997-10-17 12:53 ` Jason Merrill
1997-10-15 16:51 ` Peter Seebach
1997-10-15 14:33 ` Richard Henderson
1997-10-15 12:10 Greg Galloway
1997-10-15 20:16 ` Joe Buck
1997-10-16 12:58 ` H.J. Lu
1997-10-15 12:10 Greg Galloway
1997-10-16 12:53 ` H.J. Lu
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