g++ and null pointers

g++ and null pointers

[Eljay Love-Jensen]

Hi everyone,

GCC 3.3.1 on Cygwin

When I compile this test.cpp source...

// g++ -Wno-long-long -pedantic -Wall -W -c test.cpp
#define NULL __null
int main()
{
     void* p;
     p = 0;
     p = 0u;
     p = 0ul;
     p = 0ull;
     p = 0l;
     p = 0ll;
     p = false;
     // silly...
     p = -0;
     p = -0u;
     p = -0ul;
     p = -0ull;
     p = -0l;
     p = -0ll;
     p = -false;
     // my druthers...
     p = NULL;
     return 0;
}

...GCC is happy with all of these assignments.

Are they all supposed (ISO 14882) to be legit?  Some of them surprised me.

The negated ones are just for fun.  I didn't go completely crazy with the 
cheese whiz, and put in "!!0" and "+0" and hexadecimal, and octal, and 
various permutations of the [uUlL]* suffix.

Sincerely,
--Eljay

Re: g++ and null pointers

[Falk Hueffner]

Eljay Love-Jensen <eljay@adobe.com> writes:

> When I compile this test.cpp source...
>
> // g++ -Wno-long-long -pedantic -Wall -W -c test.cpp
> #define NULL __null
> int main()
> {
>      void* p;
>      p = 0;
>      p = 0u;
>      p = 0ul;
>      p = 0ull;
>      p = 0l;
>      p = 0ll;
>      p = false;
>      // silly...
>      p = -0;
>      p = -0u;
>      p = -0ul;
>      p = -0ull;
>      p = -0l;
>      p = -0ll;
>      p = -false;
>      // my druthers...
>      p = NULL;
>      return 0;
> }
>
> ...GCC is happy with all of these assignments.
>
> Are they all supposed (ISO 14882) to be legit?  Some of them surprised me.

The standard says that a null pointer constant is "[a]n integer
constant expression with the value 0", so these seem all OK.

-- 
	Falk