Preprocessor symbol style

Preprocessor symbol style

[Mark Kettenis]

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.

Mark

Re: Preprocessor symbol style

[Daniel Jacobowitz]

On Sat, Aug 14, 2004 at 12:02:00AM +0200, Mark Kettenis wrote:
> 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.

Full support.  I don't see a need to do it all at once, though I
wouldn't object.

-- 
Daniel Jacobowitz

Re: Preprocessor symbol style

[Eli Zaretskii]

> Date: Sat, 14 Aug 2004 00:02:00 +0200 (CEST)
> From: Mark Kettenis <kettenis@chello.nl>
> 
> #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?

I agree that the second style is more readable.

Re: Preprocessor symbol style

[Kevin Buettner]

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

Re: Preprocessor symbol style

[Michael Chastain]

These files, among others, already use #elif:

  bfd/bfdio.c	since gdb 6.1
  gdb/top.c	since gdb 5.2.1
  gdb/utils.c	since gdb 4.17

So #elif is standard, and we're already using it!
Safe as houses.

Re: Preprocessor symbol style

[Andrew Cagney]

Brain dump ...

The original requirement was for:

	|#ifdef

i.e., hard against margin, no spaces, that was eventually clarified into:

	|#

i.e., `#' hard against margin.  The ARI checks the latter.

As for coding style, can gdb_indent.sh be used to maintain this?  I'm 
reluctant to see us try to impose such an indention requirement without 
backing it with a robust and automated way of fixing / updating any files.

Andrew