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Date: Mon, 16 Aug 2004 18:58:00 -0000
From: Kevin Buettner <kevinb@redhat.com>
To: gdb@sources.redhat.com
Subject: Re: Preprocessor symbol style
Message-Id: <20040816115800.5cc7d89f@saguaro>
In-Reply-To: <200408132202.i7DM1x5k012167@elgar.kettenis.dyndns.org>
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On Sat, 14 Aug 2004 00:02:00 +0200 (CEST)
Mark Kettenis <kettenis@chello.nl> wrote:

> IIRC this has been discussed before, hopefully people forgive me
> raising the issue again.
> 
> Currently in GDB we use the following style for preprocessor stuff:
> 
> #ifdef HAVE_FOO_H
> #include <foo.h>
> #else
> #ifdef HAVE_BAR_H
> #include <bar.h>
> #ifndef HAVE_FOOBAR
> #define FOOBAR FOO(BAR)
> #endif
> #endif
> #endif
> 
> I think this style has a serious problem; it's rather difficult to see
> how the #if's and #endif's balance.  Personally I've been bitten by
> this more than once.
> 
> Many GNU projects (GCC, glibc, autoconf, coreutils) use a somewhat
> different style:
> 
> #ifdef HAVE_FOO_H
> # include <foo.h>
> #else
> # ifdef HAVE_BAR_H
> #  include <bar.h>
> #  ifndef HAVE_FOOBAR
> #   define FOOBAR FOO(BAR)
> #  endif
> # endif
> #endif
> 
> This makes it much easier to see how the #if's and #endif's balance.
> 
> Can we please adopt the second style for GDB?  We can convert things
> incrementally, or if we want to do it all at once, I'll volunteer to
> provide the mamoth patch.

I agree that your proposed change is more readable than the current
convention.  I am in favor of this reindentation.

But, since we've settled on ISO C, I think we can improve readability
even more.  How about this?

#ifdef HAVE_FOO_H
# include <foo.h>
#elif defined(HAVE_BAR_H)
# include <bar.h>
# ifndef HAVE_FOOBAR
#  define FOOBAR FOO(BAR)
# endif
#endif

One #ifdef / #endif pair has been removed by using #elif instead. 
There are cases where the use of #elif improves readability a lot more
than is apparent from this example.

Kevin