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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c++
Subject: Re: An example: code to list exports of a Windows DLL.
Date: Mon, 19 Aug 2019 18:31:54 -0700
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"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> writes:
> On 19.08.2019 21:44, Richard wrote:
>> "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> spake the secret code
>> <qi042o$if8$1@dont-email.me> thusly:
>>
>>> The $ things in the following code are macros from the specified
>>> header-only library on GitHub.
>>
>> Can you tell me where in the standard it allows for $ to be part of an
>> identifier?
>>
>> I'm looking at 5.10 in N4659 (Draft C++17) and don't see it.
>
> In the future you might risk that people think you're a total novice,
> one who doesn't even know the basics of identifiers in C++.

Then I'll risk the same thing.  Can you explain where C++17 permits $
in identifiers (or where it permits compilers to permit it)?

Earlier editions of the standard, such as C++11, permitted "other
implementation-defined characters" in identifiers.  This was dropped
after Defect Report #1963 pointed out that it was supposedly redundant.

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1963

In N4700 (a more recent C++17 draft), identifiers may contain the 52
upper and lower case letters, the 10 decimal digits, underscores, and
universal-character-names.  Characters not in the basic source character
set are mapped to universal-character-names in translation phase 1, so $
will (probably) be mapped to \u0024 .

But universal-character-names in identifiers are only allowed by
designate characters in certain ranges (Table 2 in 5.10 [lex.name]), and
\u0024 is not in any of those ranges.

For example, this program prints "42" when I compile and run it with
g++, but clang++ rejects it (it warns about the '$' in an identifier
and says that "foo" is undeclared on the "std::cout << ..." line).
(I used "-std=c++17 -pedantic" for both.)

#include <iostream>
int main() {
    const int foo$bar = 42;
    std::cout << foo\u0024bar << "\n";
}

I believe that both foo$bar and foo\u0024bar violate a diagnosable rule
and therefore require a diagnostic from any conforming compiler (which
implies that gcc is non-conforming).

It's possible that it was intended to permit (but not require) support
for $ in identifiers, but that that was overlooked in the response to
Defect Report #1963.  Perhaps 0024 should be added to Table 2?

Or perhaps I'm missing something (always a real possibility).

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */