[Development] Difficulties using Qt's new categorized logging. How to install filters?

[Mark]

On Mon, Oct 14, 2013 at 12:08 PM, Koehne Kai <Kai.Koehne at digia.com> wrote:

>
> > -----Original Message-----
> > From: development-bounces+kai.koehne=digia.com at qt-project.org
> > [mailto:development-bounces+kai.koehne=digia.com at qt-project.org] On
> > Behalf Of Mark
> > Sent: Saturday, October 12, 2013 3:41 PM
> > To: development at qt-project.org
> > Subject: [Development] Difficulties using Qt's new categorized logging.
> How
> > to install filters?
> >
> > Hi,
> >
> > I just tried fiddling with the new Qt categorized logging and am hitting
> some
> > difficulties. I've read the documentation [1] and had a discussion on
> irc (Qt-
> > Labs) about how to install a global filter.
> >
> > The documentation states:
> > // in a header
> > Q_DECLARE_LOGGING_CATEGORY(QT_DRIVER_USB)
> >
> > // in one source file
> > Q_LOGGING_CATEGORY(QT_DRIVER_USB, "qt.driver.usb")
> >
> > // usbEntries() will only be called if QT_DRIVER_USB category is enabled
> > qCDebug(QT_DRIVER_USB) << "devices: " << usbEntries();
> >
> > So the above line will only log when QT_DRIVER_USB is enabled. How do i
> > enable it? It's a new category "qt.driver.usb" so by that logic i'm
> inclined to
> > think that i need to install a new filter for this category and enable
> debugging
> > in there. That would be something like this:
> >
> > QLoggingCategory usbCategory("qt.driver.usb");
> > usbCategory.setEnabled(QtDebugMsg, true);
> >
> > Now if i do:
> > qCDebug(usbCategory) << "some logging";
> >
> >
> > Then it works as expected. But that's not what i want and not global.
> How can
> > i get the initial example to work - with QT_DRIVER_USB?
> >
> > I think it would be a good idea to update the documentation with this
> > information as well. I tried following the testcase, but that didn't
> help me
> > much in getting this working either.
>
> Hi Mark,
>
> Indeed the documentation could be more verbose about this ... I'll try to
> come up with a patch later on. Anyhow, the bottom line is that you should
> either set logging rules via
>
>
> http://doc-snapshot.qt-project.org/qt5-stable/qloggingcategory.html#setFilterRules
>
> or - if you need more control - set your own filter for categories:
>
>
> http://doc-snapshot.qt-project.org/qt5-stable/qloggingcategory.html#installFilter
>
>
> So, for your case, you could e.g. in main.cpp just add a line
>
> QLoggingCategory::setFilterRules(QStringLiteral("qt.driver.usb.debug =
> true"));
>
> Regards
>
> Kai
>

Hi Kai,

Thank you very much for your explanation! Would you also be able to provide
an example for installFilter? Since that is the one where i can't figure
out how it's supposed to work.
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