Re: [PATCH v3] NULL.3const: Add documentation for NULL

[Alejandro Colomar]

Hi Jakub,

On 7/25/22 20:57, Jakub Wilk wrote:
> * Alejandro Colomar <alx.manpages@gmail.com>, 2022-07-24, 21:19:
> > +.B "#define NULL  ((void *) 0)"
> > +.fi
> > +.SH DESCRIPTION
> > +.B NULL
> > +represents a null pointer constant.
> > +.PP
> > +According to POSIX,
> > +it shall expand to an integer constant expression with the value
> > +.B 0
> > +cast to type
> > +.IR "void *" .
>
> Might be worth noting that the cast requirement was added only in 
> POSIX.1-2008 aka SUSv4.
>
> > +.SH CONFORMING TO
> > +C99 and later;
>
> It's in C89 too.

Michael and I agreed that for new pages, we're going to ignore the C89 
standard, as almost all current code assumes C99 is available, at least 
to a certain degree of support.

The same as POSIX.1-1990 is also ignored for simplicity, and we start 
counting from POSIX.1-2001.

I'm not sure if documenting C89 provides any value (apart from 
historical curiosity, that is).

> > +.I NULL \- NULL
> > +is, surprisingly, undefined behavior, according to ISO C.
>
> FWIW, I don't find it surprising at all.

Then you might perhaps find it surprising that in C++ it's defined to be 0.


Cheers,

Alex

--
Alejandro Colomar
<http://www.alejandro-colomar.es/>

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