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Date: Sat, 12 Jan 2013 01:42:54 -0500
From: Rich Felker <>
Subject: Re: NULL

On Fri, Jan 11, 2013 at 11:56:02PM -0600, Rob Landley wrote:
> On 01/09/2013 05:02:29 AM, John Spencer wrote:
> >glibc defines NULL as __null: a magic variable supplied by GCC and
> >compatibles which always has pointer context.
> >
> >musl defines NULL to 0 in C++.
> >this is correct per the standard, but breaks a lot of software on
> >64bit archs,
> >because it promotes to int.
> The C99 standard section 7.17 defines the NULL macro as:
>   expands to an implementation-defined null pointer constant
> Which means it has pointer type. So either we can typecast it to

Nope, C is weirder than you think. A "null pointer constant" is
defined as an integer constant expression with value zero, or such an
expression cast to void *. So it need not have pointer type.

> void *, or we can rely on the LP64 standard (Linux, FreeBSD, and
> macosX all support) which says that long and pointer are always the
> same size on both 32 bit and 64 bit, so trivial fix would be #define
> NULL to (0L)

Yes, using 0L on both C and C++ is the solution I'm leaning towards..


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