Re: [Discuss-gnuradio] Converting from #ifndef/#define include guards to #pragma once globally

[Marcus Müller]

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Hi Moritz,

thanks :) I agree on the "let's not break builds for the pure beauty
of #pragma once" approach. I tried this only to find existing bugs,
and actually found very little; however, they could be completely
avoided by #pragma once, and therefore I do see value in using it. So
I humbly and slightly disagree with the "my editor does that for me"
approach.

Since I couldn't find info on which compilers are minimally necessary
to build GR, I tried to figure out on my own(0). So far, I've not
quite come to any useful point. Boost uses the classical include
guards, but adds a #pragma once only for MSVC compilers(1) so those
might really profit from that. Reading the gcc 3.4 release notes (2)
suggests that prior to 3.4, #pragma once was but deprecated -- showing
a few warnings in an ancient compiler doesn't seem to be too bad ;)

So I read on (3) and found out that in fact, #pragma once had problems
in gcc < 3.4 (3.2 being the oldest gcc I've actually witnessed in the
wild, these are not many) due to it not dealing with hard- and
symlinks properly. However, with our current source tree and build
methodology, this will not be critical. The only versions that would
actually produce warnings were some early gcc 3.3, after the problem
was found and before the pragma was un-deprecated again, so I think
you will hardly find someone using a compiler where this would do as
much as warn you that there is an deprecated pragma in use in the GNU
toolchain world.

So. The question stays the same: just *how* weird can build platforms
for GR be? I don't have a raging clue what people use on their
embedded devices where they'd actually try to compile GR 3.7 for, so I
can't really make a stand here.

Greetings,
Marcus


(0) If anyone knows how to get a non-interfering but working gcc3.2 on
a current fedora, let me know.
(1) o.O
(2) http://gcc.gnu.org/gcc-3.4/changes.html, search for #pragma once
(3) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11569
(4) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11569#c12
On 23.02.2014 20:03, Moritz Fischer wrote:
> Hi Marcus,
> 
> 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.
> 
> Happy hacking,
> 
> Moritz
> 
> [1] http://en.wikipedia.org/wiki/Pragma_once
> 
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