Re: [PATCH v3 1/4] Allow flexible array members in unions and alone in structures [PR53548]

[Qing Zhao <qing.zhao@oracle.com>]

> On Apr 30, 2024, at 15:52, Jason Merrill <jason@redhat.com> wrote:
> 
> On 4/30/24 14:49, Qing Zhao wrote:
>>> On Apr 30, 2024, at 15:45, Qing Zhao <qing.zhao@oracle.com> wrote:
>>> 
>>> 
>>> 
>>>>>  gcc/doc/extend.texi | 34 ++++++++++++++++++++++++++++++++++
>>>>>  1 file changed, 34 insertions(+)
>>>>> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
>>>>> index 7b54a241a7bf..cba98c8aadd7 100644
>>>>> --- a/gcc/doc/extend.texi
>>>>> +++ b/gcc/doc/extend.texi
>>>>> @@ -42,6 +42,8 @@ extensions, accepted by GCC in C90 mode and in C++.
>>>>>  * Named Address Spaces::Named address spaces.
>>>>>  * Zero Length::         Zero-length arrays.
>>>>>  * Empty Structures::    Structures with no members.
>>>>> +* Flexible Array Members in Unions::  Unions with Flexible Array Members.
>>>>> +* Flexible Array Members alone in Structures::  Structures with only Flexible Array Members.
>>>>>  * Variable Length::     Arrays whose length is computed at run time.
>>>>>  * Variadic Macros::     Macros with a variable number of arguments.
>>>>>  * Escaped Newlines::    Slightly looser rules for escaped newlines.
>>>>> @@ -1873,6 +1875,38 @@ The structure has size zero.  In C++, empty structures are part
>>>>>  of the language.  G++ treats empty structures as if they had a single
>>>>>  member of type @code{char}.
>>>>>  +@node Flexible Array Members in Unions
>>>>> +@section Unions with Flexible Array Members
>>>>> +@cindex unions with flexible array members
>>>>> +@cindex unions with FAMs
>>>>> +
>>>>> +GCC permits a C99 flexible array member (FAM) to be in a union:
>>>>> +
>>>>> +@smallexample
>>>>> +union with_fam @{
>>>>> +  int a;
>>>>> +  int b[];
>>>>> +@};
>>>>> +@end smallexample
>>>>> +
>>>>> +If all the members of a union are flexible array member, the size of
>>> 
>>> It’s for the following case:
>>> 
>>> union with_fam_3 {
>>>   char a[];
>>>   int b[];
>>> }
>>> 
>>> And also include:  (the only member of a union is a flexible array member as you mentioned below)
>>> 
>>> union with_fam_1 {
>>>   char a[];
>>> }
>>> 
>>> So, I think the original sentence:
>>> 
>>> “If all the members of a union are flexible array member, the size of”
>>> 
>>> Should be better than the below:
>>>> 
>>>> "If the only member of a union is a flexible array member”
>> How about the following wording?
>> "If every member of a union is flexible array member, the size of”
> 
> "is a flexible array member", sure.

Okay, will update the doc.

Thanks a lot.

Qing
> 
> Jason
>