Wireshark-dev: Re: [Wireshark-dev] Allowing use of more C99 features
From: Graham Bloice <[email protected]>
Date: Fri, 2 Sep 2016 08:54:26 +0100


On 2 September 2016 at 03:51, Guy Harris <[email protected]> wrote:
On Sep 1, 2016, at 1:14 PM, Peter Wu <[email protected]> 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