[Interest] debugging: how to get meaningful QObject information in a command line session

[Andreas Pakulat]

Hi Rene,

Thiago pointed you to QObject functions, those only work on instances of
QObject. QString does not subclass QString and hence you cannot call those
functions on a QString.

For QString debugging there's QString::toUtf8().data() which will give you
a temporary C string that can be printed.

And yes there are gdb extensions (its just a python script) that teach gdb
something about qt containers and qstring (and some other types) so you can
see them in the debugger with a simple 'p' or access their children. I'm
not sure right now wether Qt ships such a file for gdb or wether QtCreator
contains them, or maybe both.

Andreas

On Tue, May 26, 2015 at 11:40 AM, René J.V. <rjvbertin at gmail.com> wrote:

> On Monday May 25 2015 17:11:02 Thiago Macieira wrote:
>
> Thanks for the feedback:
>
> >Make the debugger call the QObject::dumpObjectInfo() and
> >QObject::dumpObjectTree() in the objects you want to get information from.
>
> I presume that would entail calling the actual function with the object
> pointer as its first argument (or something of the sort) or do you actually
> mean to compile in those calls (guess not, would be just as easy to use a
> simple qDebug() in that case)? Usually when I look at a QObject instance in
> lldb (or gdb) it knows to show so little about them that I wouldn't know
> how to call a method. A quick test under Linux with gdb and a debuggable
> executable I had lying around (built with -O3 -g) told me that "No symbol
> "QObject" in current context".
>
> On OS X:
> (lldb) p QObject::dumpObjectInfo(&fileName)
> error: call to non-static member function without an object argument
> error: 1 errors parsing expression
> (lldb) p fileName.dumpObjectInfo()
> error: no member named 'dumpObjectInfo' in 'QString'
> error: 1 errors parsing expression
> (lldb) p ((QObject*)&fileName)->dumpObjectInfo()
> (lldb)
>
>
> I seem to recall having seen a package (for Ubuntu) that suggested it
> installed some gdb extension that would enable gdb to print meaningful
> information, but I didn't have the time then to investigate immediately and
> now I cannot even remember if it was Qt specific or a more generic
> extension for C++ debugging.
>
> Thanks again,
>
> R.
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