Re: how can this code compile?

On Tue, 20 Mar 2007, Oliver Neukum wrote:

> Hi,
> 
> from urb.c::usb_kill_urb():
> 
> 	if (!(urb && urb->dev && urb->dev->bus))
> 		return;
> 
> Is this safe from a compiler point of view?

Of course it is.

> Might a compiler actually evaluate the inner expression and then invert
> the result?

You mean, evaluate "(urb && urb->dev && urb->dev->bus)"?  Yes indeed, it
might.  But in the course of evaluating that inner expression, the
execution would stop as soon as it found that urb was NULL.  That's
guaranteed by the C language.

Alan Stern


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