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

[Richard Hardgrave]

> From owner-omniorb-list@uk.research.att.com Thu Aug 23 11:56 CDT 2001
> From: "Keeley, Michael" <mkeeley@orchestream.com>
> To: "'omniorb-list@uk.research.att.com'"
	 <omniorb-list@uk.research.att.com>
> Subject: [omniORB] [omnithread] Why is NULL defined as (void*)0?
> Date: Thu, 23 Aug 2001 17:46:10 +0100
> MIME-Version: 1.0
> X-Loop: omniorb-list@uk.research.att.com
> 
> 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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