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Re: C99
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From:
H.Merijn Brand
Date:
May 18, 2021 13:28
Subject:
Re: C99
Message ID:
20210518152758.20f18634@pc09
On Tue, 18 May 2021 12:01:02 +0000, Nicholas Clark <nick@ccl4.org>
wrote:
> What are we trying to achieve:
>
> We want the developer documentation to say what C constructs are fair
> game in non-platform-specific code. This is going to be "you can use
> all of C89 plus the following", with an explicit list of useful
> features we know work.
>
> The C dialect we use is constrained by
>
> * platforms we support where the only compiler is inflexible (eg
> HP-UX)
1. The native AIX xlC compiler is even more restrictive
2. The native compiler on HP-UX is restrictive, but I'd like to note
that building *recent* GNU gcc is close to impossible on HP-UX. This
means that using the less restrictive GNU gcc on HP-UX is another
restriction on itself, as the most recent supported version is max
something like gcc-4.6.2
> * C++ extensions on CPAN need our headers, hence our headers must
> also be conformat C++
>
> We also can choose to be constrained by supporting older less flexible
> compilers on platforms where newer compilers are available. Hence
> *this* choice of C dialect is intertwined with the "platform" support
> choices.
>
>
> Where we are now:
>
> C compilers are rarely "C89 and not a penny more".
Some of them are in their default mode, but know/support run-time
options to extend into the C99 domain. As it stands, the hints files
know about those options.
> We "cheat" somewhat and already use or emulate what we need for:
>
> * bool
> * static inline
> * static assert
>
> We might be able to add this this list without needing any trade off
> between "feature" and "platform support"
>
> Likely gcc 3.1 or later is just fine:
> https://gcc.gnu.org/c99status.html
> It's the other compilers that will be "fun".
>
> Postgres has a coding standard that might be useful:
> https://www.postgresql.org/docs/13/source-conventions.html
> but curiously it says
>
> A few features included in the C99 standard are, at this time,
> not permitted to be used in core PostgreSQL code. This currently
> includes variable length arrays, intermingled declarations and
> code, // comments, universal character names. Reasons for that
> include portability and historical practices.
>
> without listing any more details about why.
>
>
> What we might like:
>
> For each C99 feature we might like, it would be useful to *tabulate*
>
> 1) how using this would improve the code
> 2) what compilers/platforms don't support this directly
> 3) can it be emulated/worked around for them
>
> that way we can make sensible trade-off decisions, and document the
> "why".
>
> I think that the list is longer than this, and I don't know the
> "hinder"/"work around" parts, but *as a start*
>
> ------------ --------------------------------------------------------
> Feature: mixed declarations and code
> Benefit: Can directly reduce line count without reducing
> readability, Can indirectly make it easier to use const
Increase readability by declaring variables for the scope/block they
are used in
> Hindered by:
> Work around:
>
> ------------ --------------------------------------------------------
> Feature: member structure initialisers
> Benefit: Clearer code.
> Less chance of errors.
> Structures can be re-ordered wit out makework.
> Hindered by: frustratingly these were only recently added to C++, so
> we couldn't use them in headers, even if we can use them
> elsewhere
> Work around:
>
> ------------ --------------------------------------------------------
> Feature: 64 bit integer types
> even if slow, and just for arithmetic and bitwise
> operators
> Benefit: certain calculations can be expressed directly
> Hindered by:
> Work around:
>
> ------------ --------------------------------------------------------
> Feature: // comments
> Benefit:
NONE!
> Hindered by:
Reduced consistency
> Work around:
Don't use it
> ------------ --------------------------------------------------------
> Feature: vararg macros
> Benefit:
> Hindered by:
> Work around:
--
H.Merijn Brand https://tux.nl Perl Monger http://amsterdam.pm.org/
using perl5.00307 .. 5.33 porting perl5 on HP-UX, AIX, and Linux
https://tux.nl/email.html http://qa.perl.org https://www.test-smoke.org
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