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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: encapsulating directory operations
Date: Fri, 23 May 2025 22:05:31 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Richard Harnden <richard.harnden@gmail.invalid> writes:
>
>> On 22/05/2025 23:32, Keith Thompson wrote:
>>
>>> "Paul Edwards" <mutazilah@gmail.com> writes:
>>>
>>>> [...]
>>>
>>> In one of your library's headers:
>>> extern const char ESCAPE;
>>> In the corresponding *.c file:
>>> const char ESCAPE = ('z' - 'a' == 25 ? '\x1b' : '\x27');
>>> Change the name if you prefer.
>>
>> Wouldn't that be a reserved identifier?
>
> Yes, it would.  Good catch.
>
> (Identifiers starting with E followed by either a digit or an uppercase
> letter are reserved;  they could be defined as macros in <errno.h>.)

They are reserved only as macros, and only if <errno.h> has
been #include'd.

For this particular use, it's easy to make the definition work,
simply by adding

    #undef ESCAPE

before the declaration in the header file, and before the
definition in the source file (assuming of course that if
there are any #include <errno.h> they precede the #undef's).