(LPVOID) NULL: unnecessary cast?

[Francois Gouget]

I have noticed a lot of constructs of the form:

HRESULT WINAPI DMUSIC_CreateDirectMusicScriptImpl (LPCGUID lpcGUID, LPVOID* ppobj, LPUNKNOWN pUnkOuter) {
   IDirectMusicScriptImpl* obj;

   obj = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(IDirectMusicScriptImpl));
   if (NULL == obj) {
     *ppobj = (LPVOID) NULL;
     return E_OUTOFMEMORY;
   }


What's the point of casting NULL to (LPVOID)? Isn't it already a void* 
anyway? Is it to fix a warning issued by ultra-recent gcc versions? (gcc 
3.4.2 does not complain here)


Similarly there are a lot of casts like this:

     *ppobj = (LPVOID)&This->UnknownVtbl;

Again I thought any kind of pointer could be assigned to a void* 
pointer so is this cast really necessary?

-- 
Francois Gouget         fgouget(a)free.fr        http://fgouget.free.fr/
         It really galls me that most of the computer power in the world
                           is wasted on screen savers.
                      Chris Caldwell from the GIMPS project
                        http://www.mersenne.org/prime.htm

[Marcus Meissner]

On Mon, Dec 13, 2004 at 02:08:31PM +0100, Francois Gouget wrote:
> I have noticed a lot of constructs of the form:
>
> HRESULT WINAPI DMUSIC_CreateDirectMusicScriptImpl (LPCGUID lpcGUID, LPVOID* 
> ppobj, LPUNKNOWN pUnkOuter) {
>   IDirectMusicScriptImpl* obj;
>
> obj = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 
>   sizeof(IDirectMusicScriptImpl));
>   if (NULL == obj) {
>     *ppobj = (LPVOID) NULL;
>     return E_OUTOFMEMORY;
>   }
>
> What's the point of casting NULL to (LPVOID)? Isn't it already a void* 
> anyway? Is it to fix a warning issued by ultra-recent gcc versions? (gcc 
> 3.4.2 does not complain here)

No, this should work as is. NULL should be able to be assigned
to any pointer.
> Similarly there are a lot of casts like this:
>
> *ppobj = (LPVOID)&This->UnknownVtbl;

> Again I thought any kind of pointer could be assigned to a void* 
> pointer so is this cast really necessary?

This is different and needs to be there.

Ciao, Marcus