Alignas broken when used with constexpr array data member for structure

Alec Teal a.teal@warwick.ac.uk
Fri Jan 12 16:50:00 GMT 2018


So I can't reproduce this via godbolt

For example both the example given and:

classX {
private:
staticconstexprintx = 5;
staticconstexprinty = 4;
public:
structalignas(y) S {
chardata[x];
};
}; BOTH give errors for me - I'm just going to leave it at this point. 
It's obviously fixed whatever it was. Thanks for your time. Alec

On 09/01/18 14:26, Mason wrote:
> On 09/01/2018 14:39, Alec Teal wrote:
>
>> In GCC 4.8.4 I have something like the following:
> FWIW, 4.8 is no longer supported (2013)
>
>> constexpr int x = 5;
>> constexpr int y = 4;
>> struct alignas(y) my_data_block {
>>      char data[x];
>> };
>>
>>
>> And it causes some weird errors to the tune of "size of array 'data' is
>> not an integral constant-expression" in the presence of the alignas
> A good support request should specify
> - exact compiler version (GCC 4.8.4)
> - a small testcase (given above)
> - exact compilation flags (missing)
> - exact error message
>
>
> Compiling the above source on godbolt using:
> gcc 4.8.4 -Wall -Wextra
>
> 1 : <source>:1:1: warning: identifier 'constexpr' is a keyword in C++11 [-Wc++0x-compat]
>   constexpr int x = 5;
>   ^
> 1 : <source>:1:1: error: 'constexpr' does not name a type
> 1 : <source>:1:1: note: C++11 'constexpr' only available with -std=c++11 or -std=gnu++11
> 2 : <source>:2:1: error: 'constexpr' does not name a type
>   constexpr int y = 4;
>   ^
> 2 : <source>:2:1: note: C++11 'constexpr' only available with -std=c++11 or -std=gnu++11
> 3 : <source>:3:19: error: expected initializer before 'my_data_block'
>   struct alignas(y) my_data_block {
>                     ^
> Compiler returned: 1
>
>
>
> Compiling the above source on godbolt using:
> gcc 4.8.4 -Wall -Wextra -std=c++11
>
> No errors.
>
>
> So it seems I can't reproduce the issue?
>
> Looking at Bugzilla as jwakely suggested turns up
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58601
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70124
>
>
> Regards.



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