Re: null argument where non-null required (argument 2)

[<sisyphus1 at optusnet dot com dot au>]

> -----Original Message----- 
> From: Ángel González
> Sent: Monday, January 28, 2013 2:17 AM
> To: sisyphus1@optusnet.com.au
> Cc: gcc-help@gcc.gnu.org
> Subject: Re: null argument where non-null required (argument 2)
>
> On 27/01/13 04:01, sisyphus1@optusnet.com.au wrote:
> > For anyone interested (and in case it might be of relevance), using
> > -Wall, I get the warning when I do:
> >
> >  if(strcmp("Math::BigInt", HvNAME(SvSTASH(SvRV(x))))) { .... }
> >
> > yet, if I break that into 2 lines:
> >
> >  const char * h = HvNAME(SvSTASH(SvRV(x)));
> >  if(strcmp("Math::BigInt", h)) { .... }
> >
> > no such warning is emitted.
>
> What's the expansion of HvNAME(SvSTASH(SvRV(x)));  ? Is it possible that
> it expands to a conditional which in one of the branches returns null?
> (although never taken in this specific instance)

I would think that is so. (I haven't actually waded through the plethora of 
macros, but I would be very surprised if that's not the case.)
In many instances it *does* return null.

Would that be all that's needed to trigger the warning ?
If so, what are my options regarding silencing the warning ?

There's no such warning if I do:

/* x is an int arg passed to the sub - could be any value */
 const char *h = x == 0 ? NULL : "Math::BigInt";
 if(strcmp("Math::BigInt", h)) { .... }

And there's not even a warning if I do:

 const char *h = NULL;
 if(strcmp("Math::BigInt", h)) { .... }

Thanks for the reply, Ángel.

Cheers,
Rob