[omniORB] [omnithread] Why is NULL defined as (void*)0?

[Keeley, Michael]

Hmm,

I don't agree with your definition of the convention of using NULL.
NULL is supposed to refer to a pointer that does not refer to an object;
which does not preclude it from being used in assignment or return
statements.

In Stroustrop's C++ (3rd ed) p5.1.1 he even recommends defining NULL as

const int NULL = 0;

He also says that "Because of C++'s tighter type-checking, the use of a
plain 0, rather than any suggested NULL macro, leads to fewer problems."

MikeK.

-----Original Message-----

> 
> In the omnithread.h header, NULL is defined to be (void*)0.
> 
> Shouldn't this be just 0?
> Otherwise code such as
> 
> #define NULL (void*) 0
> 
> char* foo() {
>   return NULL;
> }

I believe you are a bit confused about the convention for
using NULL.  It's used in making comparisons with pointers
to objects of unknown type.  E.g.:

if ( foo() == NULL ) { ... };

(The void* gets caste to a char* for the comparison.)

No compiler will allow you to return a different "type"
than you have declared it to return.  If your function wanted
to return a long*, you would still have to caste it to
a char* before returning it.

Richard

There's altogether too much blood in my caffeine system. 8^)

> 
> will not compile - void* cannot be cast to char*.
> 
> Mike.
> 
> Michael Keeley


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