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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c
Subject: Re: "A diagram of C23 basic types"
Date: Sat, 5 Apr 2025 17:36:15 +0200
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On 05/04/2025 04:15, Keith Thompson wrote:
> James Kuyper <jameskuyper@alumni.caltech.edu> writes:
>> Muttley@dastardlyhq.org wrote:
>>> On Wed, 2 Apr 2025 14:12:18 -0000 (UTC)
>>> antispam@fricas.org (Waldek Hebisch) wibbled:
>> ...
>>>> C99 has VMT (variable modified types).  Thanks to VMT and complex types
>>>> C99 can naturaly do numeric computing that previously was done using
>>>> Fortran 77.  Offical C++ has no VMT.  C++ mechanizms look nicer,
>>>
>>> Officially no, but I've never come across a C++ compiler that didn't support
>>> them given they're all C compilers too.
>>
>> There exist many programs that can compile either C code and C++ code,
>> depending either upon the extension of the file name or explicit command
>> line options to determine which language's rules to apply. That doesn't
>> qualify. Do you know of any compiler that accepts VMTs when compiling
>> according to C++ rules? If so, please provide an example. It will help
>> if the code has some features that are well-formed code in C++, but
>> syntax errors in C, to make it clear that C++'s rules are being implemented.
> 
> g++ and clang++ both do so:
> 
> int main() {
>      class foo { };
>      int len = 42;
>      int vla[len];
> }
> 
> Both warn about the variable length array when invoked with "-pedantic"
> and reject it with "-pedantic-errors".
> 

There are also things that are VLA's in C, but ordinary arrays in C++, 
and acceptable in both languages :

int main() {
	const int len = 42;
	int arr[len];
}


> Microsoft's C and C++ compilers do not support VLAs.  (Their C compiler
> never supported C99, and VLAs were made optional in C11, so that's not a
> coformance issue.)
>