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Invalid sample definition for errno

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  Invalid sample definition for errno Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-19 18:08 -0800
    Re: Invalid sample definition for errno Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-11-20 05:26 -0800
      Re: Invalid sample definition for errno Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-20 13:58 -0800

#6451 — Invalid sample definition for errno

A footnote in the section describing <errno.h> says:

    The macro errno need not be the identifier of an object. It might
    expand to a modifiable lvalue resulting from a function call (for
    example, *errno()).

Footnotes are non-normative, and this one is presumably intended to be
informal, but that's not a valid macro definition for errno, both
because it's not fully protected by parentheses and because the function
can't be named "errno".

A valid definition (and the one used by glibc) is:

    # define errno (*__errno_location ())

I suggest the footnote should be updated to use something like that
(though it needn't show the entire #define directive).

The same wording appears starting in C90 and up to and including the
latest C23 draft.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */

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#6452

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> A footnote in the section describing <errno.h> says:
>
>     The macro errno need not be the identifier of an object.  It might
>     expand to a modifiable lvalue resulting from a function call (for
>     example, *errno()).
>
> Footnotes are non-normative, and this one is presumably intended to be
> informal, but that's not a valid macro definition for errno, both
> because it's not fully protected by parentheses and because the function
> can't be named "errno".

I see no reason the function couldn't be named "errno".

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#6453

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>> A footnote in the section describing <errno.h> says:
>>
>>     The macro errno need not be the identifier of an object.  It might
>>     expand to a modifiable lvalue resulting from a function call (for
>>     example, *errno()).
>>
>> Footnotes are non-normative, and this one is presumably intended to be
>> informal, but that's not a valid macro definition for errno, both
>> because it's not fully protected by parentheses and because the function
>> can't be named "errno".
>
> I see no reason the function couldn't be named "errno".

My thought was that giving the function and the macro the same name
would cause a conflict, and I thought I had an example that demonstrated
it.  Looking again, I was mistaken:

    If the name of the macro being replaced is found during this scan of
    the replacement list (not including the rest of the source file’s
    preprocessing tokens), it is not replaced.

I still suggest that using the same name for both is needlessly
confusing.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */

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