Re: Allowing use of more C99 features

[Graham Bloice <graham.bloice () trihedral com>]

On 2 September 2016 at 03:51, Guy Harris <guy () alum mit edu> wrote:

> On Sep 1, 2016, at 1:14 PM, Peter Wu <peter () lekensteyn nl> wrote:
>
> > Patch https://code.wireshark.org/review/17421 will allow use of some C99
> > features in master (future 2.4):
>
> For UN*X, with autotools:
>
>         The AC_PROG_CC_C99 macro is used, and, if it fails to enable what
> it considers "C99 mode" for the compiler, the configure script will fail.
> This means some older compilers may not be supported; it's probably time to
> drop those compilers.  The macro appears to try to enable it for:
>
>                 GCC (and Clang), using -std=gnu99
>                 IBM XL C, using -qlanglvl=extc99
>                 HP cc, using -AC99
>                 Intel ICC, using -std=c99
>                 SGI's C compiler for IRIX, using -c99
>                 Sun/Oracle's C compiler, using -xc99=all
>                 DEC/Compaq/HP's C compiler for Alpha on Tru64, using -c99
>
>         so you're out of luck if you have a version of those compilers
> that doesn't support those flags and doesn't support all of:
>
>                 _Bool, // comments, flexible array members, inline, signed
> and unsigned long long int, mixed code and declarations, named
> initialization of structs, restrict, va_copy, varargs macros, variable
> declarations in for loops, and variable length arrays
>
> For UN*X, with CMake:
>
>         I'm not sure whether it'll properly enable C99 support for all of
> the compilers in question.
>
> For Windows (CMake assumed), MSVC 2013 supports:
>
>         // comments as long as you don't compile with /Za, but there might
> be a warning to suppress;
>
>         flexible arrays, but there's a warning to suppress, which this
> change suppresses;
>
>         inline functions - it might require __inline rather than inline,
> but GLib is #defining inline to be __inline with MSVC, so we can just use
> "inline";
>
>         mixed code and declarations, but there's a bug that might or might
> not hit us:
>
>                 https://connect.microsoft.com/
> VisualStudio/feedback/details/808650/visual-studio-2013-c99-compiler-bug
That particular example seems to have been fixed, at least for me with
VS2013 Update 5.


>         named initialization of structs, but there's a bug that might or
> might not hit us:
>
>                 https://connect.microsoft.com/
> VisualStudio/feedback/details/805981


That particular example seems to have been fixed, at least for me with
VS2013 Update 5.


>         varargs macros, which we're already using;
>
>         variable declarations in for loops, apparently:
>
>                 http://stackoverflow.com/questions/21696983/error-on-
> declaring-variable-in-for-statement
>
> so, in addition to
>
> > - flexible array members
> > - trailing comma in enum declarations
> > - inline function keyword
>
> we also can use // comments and, apparently, variable declarations in for
> loops, assuming there's no bug that gets in the way.  *If* we avoid the
> bugs, we can also use mixed code and declarations and named initialization
> of structs.

-- 
Graham Bloice

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