> On Aug 31, 2022, at 3:29 PM, Joseph Myers <jos...@codesourcery.com> wrote:
>
> On Wed, 31 Aug 2022, Qing Zhao via Gcc-patches wrote:
>
>>> How is level 3 (thus -fstrict-flex-array) interpreted when you specify
>>> -std=c89? How for -std=gnu89?
>>
>> 1. what’s the major difference between -std=c89 and -std=gnu89 on flexible
>> array? (Checked online, cannot find a concrete answer on this).
>> ** my understanding is: -std=c89 will not support any flexible array
>> (neither [], [0], [1]), but -std=gnu89 will support [0] and [1], but not [].
>> Is this correct?
>
> Flexible array members are supported in all C standard modes, since they
> don't affect the semantics of any valid pre-C99 program (only make valid
> programs that were previously erroneous).
>
> With -std=c89 or -std=gnu89, -pedantic will give a warning "ISO C90 does
> not support flexible array members" and -pedantic-errors will change that
> to an error.
A little confused here…
With both -std=c89 and -std=gnu89, -pedantic will warning on “[]” (C99 flexible
array member):
[opc@qinzhao-ol8u3-x86 ~]$ gcc -std=c89 t.c -pedantic
t.c:5:7: warning: ISO C90 does not support flexible array members [-Wpedantic]
5 | int b[];
| ^
[opc@qinzhao-ol8u3-x86 ~]$ gcc -std=gnu89 t.c -pedantic
t.c:5:7: warning: ISO C90 does not support flexible array members [-Wpedantic]
5 | int b[];
| ^
Does the above mean that -std=gnu89 does not support C99 flexible array member,
then
When -std=gnu89 + -fstrict-flex-array=3 (ONLY C99 flexible array member [] is
treated as a valid flexible array) present together,
It should be reasonable to issue warning on this? (-fstrict-flex-arrays=3
is not supported by GNU extension GNU89, ignored)
Right?
Qing
>
> --
> Joseph S. Myers
> jos...@codesourcery.com
