Em Thu, 04 Jun 2009 17:20:50 +0800
"figo.zhang" <figo.zhang@xxxxxxxxxxxxx> escreveu:
> On Thu, 2009-06-04 at 11:18 +0200, Laurent Pinchart wrote:
> > Hi,
> >
> > On Thursday 04 June 2009 06:20:07 figo.zhang wrote:
> > > The function video_register_device() will call the
> > > video_register_device_index(). In this function, firtly it will do some
> > > argments check , if failed,it will return a negative number such as
> > > -EINVAL, and then do cdev_alloc() and device_register(), if success return
> > > zero. so video_register_device_index() canot return a a positive number.
> > >
> > > for example, see the drivers/media/video/stk-webcam.c (line 1325):
> > >
> > > err = video_register_device(&dev->vdev, VFL_TYPE_GRABBER, -1);
> > > if (err)
> > > STK_ERROR("v4l registration failed\n");
> > > else
> > > STK_INFO("Syntek USB2.0 Camera is now controlling video device"
> > > " /dev/video%d\n", dev->vdev.num);
> > >
> > > in my opinion, it will be cleaner to do something like this:
> > >
> > > err = video_register_device(&dev->vdev, VFL_TYPE_GRABBER, -1);
> > > if (err != 0)
> > > STK_ERROR("v4l registration failed\n");
> > > else
> > > STK_INFO("Syntek USB2.0 Camera is now controlling video device"
> > > " /dev/video%d\n", dev->vdev.num);
> >
> > What's the difference ? (err != 0) and (err) are identical.
> >
> > Best regards,
> >
> > Laurent Pinchart
>
> yes, it is the same, but it is easy for reading.
if (err) is easier for reading, since it is closer to the natural language.
Also, as CodingStyle says, "C is a Spartan language". So, using just if (err)
is better than if (err != 0).
Also, since positive values don't indicate errors (on Linux, all errors are
negative values), using err != 0 looks wrong. Yet, changing they to err < 0
would require a careful review of the returned values by each function.
In summary, for newer code, the better is to always use if (err < 0), being
sure that the called function will return a negative value. However, I don't
see much sense on changing the current code.
Cheers,
Mauro
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