[PyQt] CoreDump when calling slot with 'const char*' arguement

Alexis Boutillier alexis.boutillier at arteris.com
Tue Apr 14 16:45:50 BST 2009

Hi again,

I was able to work around the problem by wrapping the signal arround 
another one using QString instead of const char *.


Alexis Boutillier a écrit :
> Hi,
> The same code was working well in PyQt 4.4.4. with Qt 4.4.3.
> We found this problem in the process of migrating to new version 4.5 of 
> Qt using PyQt snapshot.
> While reading the comments and documentation, I understand that QString 
> and QByteArray have better support (encoding, ...). The problem is that 
> this code is not  writen by us and so I can't easily change the signal 
> types.
> I will try to do a wrapper to use QString instead of char *.
> Thanks for the response.
> Phil Thompson a écrit :
>> On Thu, 09 Apr 2009 19:29:18 +0200, Alexis Boutillier
>> <alexis.boutillier at arteris.com> wrote:
>>> Hi,
>>> I'm having a core dump when connecting a signal define in a PyQt 
>>> wrapped c++ class to a python method.
>>> The c++ signal have (const char*, int, int, int, int) as arguments.
>>> I investigate the core and found that the problem is in the 
>>> conversion from c++ types to python types:
>>> in #11 0x00726c94 in PyQtProxy::invokeSlot (slot=@0x91104f4, 
>>> qargs=0xbfffac24) at qpycore_pyqtproxy.cpp:444
>>> A tuple is filed with the C++ element converted to python.
>>> Looking at the element in the tuple, the "int" are correctly added 
>>> but the "const char *" is not (can't print it with 
>>> PyString_AsString(PyObject_Repr)))
>>> Looking further, in PyObject *Chimera::toPyObject(void *cpp) const,
>>> The "int" parameters have the metatype 2 corresponding to 
>>> QMetaType::Int which is OK
>>> But the "const char *" have metatype 256 which is 
>>> PyQt_PyObject::metatype
>>> Looking at what was done in PyQt 4.4.4, in PyQt 4.5.xxxx there is no 
>>> call to PyString_FromString to convert a "const char*" is it done by 
>>> the sipConvertFromType(cpp, _type, 0);
>>> Can someone help me for where to continue investigate this problem ?
>> Is this new code or did it work with PyQt v4.4.4?
>> I'm not sure yet what the right behaviour is in this case ( need to think
>> about it), but I think you can avoid the problem with a better API. You
>> should use either QString or QByteArray instead of const char *. That 
>> would
>> mean that you can safely use the signal across threads and not have to
>> worry about who owns the underlying data and whether it remains valid.
>> Phil

Boutillier Alexis
Methodology engineer

Arteris SA
The Network-on-Chip Company TM

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Alexis.Boutillier at arteris.net

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