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(Sam Holden) wrote in message news:< >...
> On 23 Jun 2003 05:22:14 -0700, Gopi Subramanian <> wrote:
> > I am porting a c++ source from suse linux to windows,and my code does
> > a lot of binary file manipulation, during a debug session found that
> > NULL values are different in VC ++ and g++, VC++ defines NULL as 0 and
> > g++ defines it as a (void *) 0, is there any way to make sure that
> > both of them matches ?
>
> g++ should be using 0 as well. Are you sure you are using g++ and not gcc?
> Are you sure the compiler knows the code is C++ and not C.
>
> The g++ I use, has the following in the header file that defines NULL:
>
> #undef NULL
> #if defined(__cplusplus)
> #define NULL 0
> #else
> #define NULL ((void *)0)
> #endif

I use gcc 2.95.3 and the definition i have in stdef.h is

if defined (_STDDEF_H) || defined (__need_NULL)
#undef NULL /* in case <stdio.h> has defined it. */
#ifdef __GNUG__
#define NULL __null
#else /* G++ */
#define NULL ((void *)0)
#endif /* G++ */
#endif /* NULL not defined and <stddef.h> or need NULL. */
#undef __need_NULL

On 24 Jun 2003 23:39:27 -0700, Gopi Subramanian <> wrote:
> (Sam Holden) wrote in message news:< >...
>> On 23 Jun 2003 05:22:14 -0700, Gopi Subramanian <> wrote:
>> > I am porting a c++ source from suse linux to windows,and my code does
>> > a lot of binary file manipulation, during a debug session found that
>> > NULL values are different in VC ++ and g++, VC++ defines NULL as 0 and
>> > g++ defines it as a (void *) 0, is there any way to make sure that
>> > both of them matches ?
>>
>> g++ should be using 0 as well. Are you sure you are using g++ and not gcc?
>> Are you sure the compiler knows the code is C++ and not C.
>>
>> The g++ I use, has the following in the header file that defines NULL:
>>
>> #undef NULL
>> #if defined(__cplusplus)
>> #define NULL 0
>> #else
>> #define NULL ((void *)0)
>> #endif
>
> I use gcc 2.95.3 and the definition i have in stdef.h is
>
> if defined (_STDDEF_H) || defined (__need_NULL)
> #undef NULL /* in case <stdio.h> has defined it. */
> #ifdef __GNUG__
> #define NULL __null
> #else /* G++ */
> #define NULL ((void *)0)
> #endif /* G++ */
> #endif /* NULL not defined and <stddef.h> or need NULL. */
> #undef __need_NULL

Upgrade to a version which actually tries to follow the C++ standard a little...

It's free software after all

--
Sam Holden

Sam Holden wrote:

> On Wed, 25 Jun 2003 10:30:29 -0400, Ron Natalie <> wrote:
<snip>
>>
>>What's that supposed to mean? Both the versions posted are explicitly
>>permitted by the standard (and the latter definition is pretty close to the
>>latest version if not identical).
>
> #define NULL ((void *)0)
>
> is *not* permitted by the standard.
>
> After all it would make
>
> int *pi = NULL;
>
> illegal, which is certainly isn't.

I recall reading that one of the recent compilers (possibly one of the
GNU ones?) had an option to use a class similar to this:

--------------
struct null_t
{
template<typename T>
operator T*() const
{
return 0;
}

template<typename T>
operator ==(const T* rhs) const
{
return 0 == rhs;
}
};

template<typename T>
operator ==(const T* lhs, const null_t& rhs)
{
return 0 == lhs;
}

#undefine NULL
null_t NULL;
--------------

It's certainly interesting. Stops NULL from being used outside of
pointer operations, which of course breaks the standard, but can still
be implicitly converted to and compared against any pointer type. I
have't checked to see what the various compilers make of it from a code
generation and optimization standpoint, but it looks interesting.

--
Corey Murtagh
The Electric Monk
"Quidquid latine dictum sit, altum viditur!"

"Sam Holden" <> wrote in message news:. ..
> On Wed, 25 Jun 2003 10:30:29 -0400, Ron Natalie <> wrote:
> >
> > "Sam Holden" <> wrote in message news:. ..
> >
> >>
> >> Upgrade to a version which actually tries to follow the C++ standard a little...
> >>
> >> It's free software after all
> >>
> >
> > What's that supposed to mean? Both the versions posted are explicitly
> > permitted by the standard (and the latter definition is pretty close to the
> > latest version if not identical).
>
> #define NULL ((void *)0)
>
> is *not* permitted by the standard.
>
Yes and if you looked at the inclusion it DOES NOT define it that way.
Did you see all that ifdef stuff in there? It keeps the cast off the C++ code.

On Thu, 26 Jun 2003 08:58:02 -0400, Ron Natalie <> wrote:
>
> "Sam Holden" <> wrote in message news:. ..
>> On Wed, 25 Jun 2003 10:30:29 -0400, Ron Natalie <> wrote:
>> >
>> > "Sam Holden" <> wrote in message news:. ..
>> >
>> >>
>> >> Upgrade to a version which actually tries to follow the C++ standard a little...
>> >>
>> >> It's free software after all
>> >>
>> >
>> > What's that supposed to mean? Both the versions posted are explicitly
>> > permitted by the standard (and the latter definition is pretty close to the
>> > latest version if not identical).
>>
>> #define NULL ((void *)0)
>>
>> is *not* permitted by the standard.
>>
> Yes and if you looked at the inclusion it DOES NOT define it that way.
> Did you see all that ifdef stuff in there? It keeps the cast off the C++ code.

Here's the snippet:

if defined (_STDDEF_H) || defined (__need_NULL)
#undef NULL /* in case <stdio.h> has defined it. */
#ifdef __GNUG__
#define NULL __null
#else /* G++ */
#define NULL ((void *)0)
#endif /* G++ */
#endif /* NULL not defined and <stddef.h> or need NULL. */
#undef __need_NULL

Surely G++ is the indicator for the c++ path...

And hence #define NULL ((void *)0) is defined for c++ code.

if not, then whomever thought labelling the non c++ path as G++ must
have a very strange outlook on the world.

--
Sam Holden

> if defined (_STDDEF_H) || defined (__need_NULL)
> #undef NULL /* in case <stdio.h> has defined it. */
> #ifdef __GNUG__
> #define NULL __null
> #else /* G++ */
> #define NULL ((void *)0)
> #endif /* G++ */
> #endif /* NULL not defined and <stddef.h> or need NULL. */
> #undef __need_NULL
>
> Surely G++ is the indicator for the c++ path...
>
> And hence #define NULL ((void *)0) is defined for c++ code.
>
> if not, then whomever thought labelling the non c++ path as G++ must
> have a very strange outlook on the world.

Actually, you are wrong. __GNUG__ is defined when G++ is compiling
a file. the __null is a magic token which resolves to the null pointer constant
(implemenation specific).

The comments after the #else and #endif just mark the entire conditional
block as being dependent on G++.