Macros and optionally NULL parameters

[David Keppel]

I'm having trouble #defining a macro that takes an argument
that should be dereferenced and set if not NULL, otherwise
not dereferenced.  More accurately, I can do it, but it doesn't
"feel right".

Wanted:

    x = ZORCH( v, p );
    y = ZORCH( v, NULL );

I tried:

    #define ZORCH( v, p ) \
	((p)?((*(p))=(v->size)):0, f(v->bork))

This works when p really points at something.  Neither pcc nor gcc
will compile it when p is NULL (on an Ultrix VAX, anyway).  Thinking
"aha! a cast behaves like an assignment to an anonymous variable",
I tried the following, which is uglier but does seem to work:

    #define ZORCH( v, p ) \
	((p)?((*((unsigned int *)p))=(v->size)):0, f(v->bork))

Ok, great.  It works.  It seems wierd to me, and that probably
means that I don't understand something.  Comments?

(Please e-mail)

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