Oh #pragma once - that old chesnut: if you have a few hours you can follow
the various discussions on stackoverflow on it. I think it is at least
enlightening to read through this answer on why it is *not* part of the ISO
C/C++ standards: http://stackoverflow.com/a/1696194
I will note that on MSVC people have found compile-time improvements by
using #pragma once - although it tends to only be noticeable in
pathological cases. Still - an important feature for people going through
the edit/compile/debug cycle.
My personal opinion on this is if there is a change to be made, it should
be to use both: prepend #pragma once to header, and still include the
#ifndef/#endifs that are present: it takes advantage of the speedup for
compilers that don't automagically recognize #ifndef/#endif header guards
(e.g. non-GCC compilers), while simultaneously it doesn't rely on
non-standard compliant compiler features (which I'll argue we don't want to
introduce *new* non-standard things into the codebase).
I'm all for doing things that decrease bugs due to bad copy/paste errors
(especially since I seem to make those types of mistakes all the time), but
relying on any compiler feature that is not part of the standard should be
be *very* carefully considered. We support too many
platform/compiler-combinations to take such things lightly.
Doug
On Sun, Feb 23, 2014 at 2:52 PM, Michael Dickens
<michael.dick...@ettus.com>wrote:
> I'll second what Moritz wrote: Since this pragma is "non standard but
> widely supported", let's stick with the header guards since they are
> guaranteed to work even with very old C / C++ compilers ... if someone
> wants to -also- use this pragma that's fine; having both should not hurt.
> I'd prefer to not rely on just the pragma ... my US$0.02 worth, if even
> that much ;) - MLD
>
> On Feb 23, 2014, at 2:03 PM, Moritz Fischer <moritz.fisc...@ettus.com>
> wrote:
> > some quick Google research found several contradictory sources. [1]
> > calls it 'non standard but widely supported'.
> > Since we build on weird platforms I think we should make absolutely
> > sure that this is the way things should be done ^{TM}.
> > Some other sources listed this as a potential speedup for compilation
> > on Visual Studio. Discuss.
> >
> > Personally I don't have an issue with header guards because there
> > exist plenty of plugins for {vim,emacs, whatever},
> > to do it for you.
>
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--
Doug Geiger
doug.gei...@bioradiation.net
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