[PATCH v3] ungetc: Guarantee single char pushback

[Florian Weimer]

* Siddhesh Poyarekar:

> On 2024-12-08 20:40, Maciej W. Rozycki wrote:
>> On Fri, 6 Dec 2024, Siddhesh Poyarekar wrote:
>> 
>>> The C standard requires that ungetc guarantees at least one pushback, so
>>> put a single byte pushback buffer in the FILE struct to enable that.
>>   So what would the problem be if we instead replaced:
>>    int _flags2;
>> with
>>    short int _flags2;
>>    char _short_backupbuf[1];
>>    char _unused;
>
> I don't see an actual problem other than that of an application maybe
> using the upper bits of _flags2 for their own logic.  One could make
> the same argument for unused2, but the defence there is that there's
> precedent of struct expansion into unused2; the same can't be said
> about _flags2.
>
> I personally don't care to retain such abuses, so it seems OK to
> shrink _flags2.  Florian, what do you think?

>From my perspective, either way is fine.

Thanks,
Florian