[cfe-dev] Variable length arrays with initialization

[Aaron Ballman via cfe-dev]

On Thu, Mar 8, 2018 at 2:47 AM, Frank Redeker via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
> Hello list,
>
> Given the following piece of code
>
> int foo (int i) {
>    char  array[i+1] = {0};
>
>    if (array[i]) {
>       return 0;
>    }
>    return 1;
> }
>
>
> When compiling with g++ [g++ (GCC) 6.4.0] the code compiles OK.
>
> But when compiling with clang++ [clang version 4.0.1
> (tags/RELEASE_401/final)] I get the following error.
>
> array.c++:2:17: error: variable-sized object may not be initialize
>
>
> My question now is, is this an bug in GCC, or is there an option for
> CLANG to compile this code without errors? Or may is there an option for
> g++ to let the compile fail on this code?

C17 6.7.9p3 says:
The type of the entity to be initialized shall be an array of unknown
size or a complete object type that is not a variable length array
type.

Clang is correct to diagnose that code. When I try out various
versions of GCC, they also diagnose your code example
(https://godbolt.org/g/Djf5iG) so I'm not certain what's happening
with your version of GCC.

~Aaron

>
>
> Frank
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