From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <ee9e417a0511120517x32c84b18w1c7062bf3e298ea@mail.gmail.com>
Date: Sat, 12 Nov 2005 08:17:45 -0500
From: Russ Cox <rsc@swtch.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] USED() macro
In-Reply-To: <0127f0e483812bde9207dcadeb8a009f@terzarima.net>
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> Does it mean that USED() can only be applied on variables of "scalar
> types"? But r is of a struct type in

yes.

>
>         void
>         drawresizewindow(Rectangle r)
>         {
>                 USED(r);
>
>                 bad();
>         }
>
> in $PLAN9/src/libdraw/nowsys-wsys.c.
>
> When compiling, 9c complains on that. A bug? Or an extension of Plan 9's
> C dialect?

In Plan 9's C compiler, USED is known to the compiler.
It makes the compiler insert a use of the variable right
there to silence used and not set warnings.

In the ports, it's a clumsy macro trying to have the same
effect.

> perhaps it could use if(&x) instead of if(x)
> to cope with structures as well

I tried this once, but then some (too smart for their
own good) compilers complain that the value is never used.

Russ