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Re: invalid universal character gives error even after #if 0

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On 2022-08-31, Philipp Klaus Krause <pkk@spth.de> wrote:
> I noticed that current gcc and clang give an error on the following:
>
> #if 0
> \u003a
> #endif
>
> but not on
>
> /*
> \u003a
> */
>
> While I see that \u003a is a constraint violation, I do not see how it 
> follows from the standard that this is a constraint violation even 
> inside #if 0.

#if 0 isn't a commenting mechanism. The material excluded by #if 0
has to consist of valid preprocessor tokens, so any token-level
constraint violations apply. E.g. you can't have an unterminated
literal in there:

#if 0
"unterminated
#endif

A universal characcter name is a constituent of an identifier,
and an identifier is a kind of preprocessing-token (in the
early translation stages) which later becomes a token.

> By a quick look at the standard it seems to me that the constraint on 
> universal character names would be treated the same as e.g. the 
> constraint on constants having a type and the value being in the 
> representable range. But I don't think anyone would expect an error on a 
> long sequence of digits inside an #if 0.

Inside an #if 0, a sequence of digits is a pp-number. This is a special
category. It doesn't have any constraints on its number of digits and
such. C99 said that "A preprocessing number does not have type or a
value; it acquires both after a successful conversion (as part of
translation phase 7) to a floating constant token or an integer constant
token."

The situation is different with identifiers. The identifier grammar
symbol is shared by preprocessor-token and token. So any constraints
that apply to some constituent of an identifier apply whether
it is part of an identifier that is either preprocesor-token or a token.

When it comes to numbers, the preprocessor-token category has the
pp-number, and token has the constant. Only when a pp-number becomes
a constant is there are problem with the range of its content.

Or something like that.

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal

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invalid universal character gives error even after #if 0 Philipp Klaus Krause <pkk@spth.de> - 2022-08-31 08:28 +0200
  Re: invalid universal character gives error even after #if 0 Kaz Kylheku <480-992-1380@kylheku.com> - 2022-08-31 06:52 +0000
    Re: invalid universal character gives error even after #if 0 Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-09-13 07:52 -0700
  Re: invalid universal character gives error even after #if 0 Siri Cruise <chine.bleu@yahoo.com> - 2022-08-31 02:13 -0700
    Re: invalid universal character gives error even after #if 0 Kaz Kylheku <480-992-1380@kylheku.com> - 2022-08-31 16:51 +0000
      Re: invalid universal character gives error even after #if 0 Siri Cruise <chine.bleu@yahoo.com> - 2022-08-31 10:57 -0700
  Re: invalid universal character gives error even after #if 0 Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-09-13 07:54 -0700

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