Subject: Re: NULL return value checking
To: Gary Thorpe <firstname.lastname@example.org>
From: Greg A. Woods <email@example.com>
Date: 04/24/2002 04:13:00
[ On Tuesday, April 23, 2002 at 18:44:20 (-0400), Gary Thorpe wrote: ]
> Subject: Re: NULL return value checking
> I have always seen NULL defined as 0.
I've seen "(void *)0" in several compilers, but it caused far more
problems than it solved and I've always undef'ed it and reset it to just
plain "0" (zero that is) in my code..... :-)
> However, NULL simply represents an
> invalid value for a pointer, and its actually value is PLATFORM SPECIFIC as
> far as ANSI compliant code goes. That is, a platform can define NULL to be
> any value which the platform would interprit to be an invalid pointer. NULL
> is usually zero because the first address in memory is usually never
> referenced or reserved.
I don't think that's true. Can you quote chapter and verse on that? (I
don't have a copy of the ANSI standard...)
> Assuming it is zero is technically incorrect. It *could* be non-zero, in
I'm pretty sure that's not true.
I do have a copy of the ISO/IEC 9899:1999 document, and it says quite
An integer constant expression with the value 0, or such an
expression cast to type (void *), is called a "null pointer
constant." If a null pointer constant is converted to a pointer
type, the resulting pointer, called a "null pointer," is guaranteed
to compare unequal to a pointer to any object or function.
I.e. no matter how it's defined, NULL == 0.
Greg A. Woods
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