[PyQt] Segfault when using QString as a function argument

[Phil Thompson]

On 26/09/2014 8:25 pm, Will Ware wrote:
> I am trying to SIP-wrap some things, with various degrees of success, 
> being
> new to the whole Qt4/PyQt/SIP world. I'm on a Mac. The issue I am 
> running
> into is in trying to wrap a pretty simple C++ function, which looks 
> like
> this:
> 
> bool InitializeApplication(QString applicationName);

You don't say but I'm assuming Python3 rather than Python2.

That particular argument declaration is extremely rare as far as PyQt is 
concerned - so may be buggy.

Unless the function is going to modify applicationName then you would 
expect it to be const QString& (which is a very common declaration).

Can you change your .sip file and the library you are wrapping to use 
const QString&? If the problem goes away then it's a PyQt bug. If not 
then it's likely to be a bug in your .sip files.

Phil

> The issue appears to be some kind of mismatch (toolchain? Qt version?
> I'm not sure) between the Qt library which would define a SIP wrapper
> for QString, and my own stuff. The error message looks like this.
> 
> Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
> 0   ???                           0x000000bb0000024d 0 + 803158884941
> 1   sip.so                         0x000000010ebc4140
> sip_api_convert_to_type + 245
> 2   sip.so                         0x000000010ebce0b5 parsePass2 + 3985
> 3   sip.so                         0x000000010ebcadb6 parseKwdArgs + 
> 322
> 4   sip.so                         0x000000010ebc81f9 
> sip_api_parse_args +
> 151
> 5   etools.so                     0x000000010db50ee4
> func_InitializeApplication(_object*, _object*) + 116
> (.sipetoolscmodule.cpp:192)
> 6   org.python.python             0x000000010d7d914d PyEval_EvalFrameEx 
> +
> 8080
> 7   org.python.python             0x000000010d7d7093 PyEval_EvalCodeEx 
> +
> 1641
> 8   org.python.python             0x000000010d7d6a24 PyEval_EvalCode + 
> 54
> 9   org.python.python             0x000000010d7f5c2c 0x10d757000 + 
> 650284
> 10  org.python.python             0x000000010d7f5cd3 PyRun_FileExFlags 
> + 137
> 11  org.python.python             0x000000010d7f5821
> PyRun_SimpleFileExFlags + 718
> 12  org.python.python             0x000000010d806363 Py_Main + 2995
> 13  libdyld.dylib                 0x00007fff8830d5fd start + 1
> 
> Apparently the Mac is a GDB-hostile platform, so I've relied on print
> statements to learn that there is a field called "mtd_cto" defined in
> siplib/sip.h as part of sipMappedTypeDef, which is a function pointer 
> used
> to convert a native type (such as QString, in this instance) to a 
> Python
> object, and the function being pointed to is somehow incompatible with 
> the
> code I compiled myself.
> 
> Has anybody run into anything like this? Any suggestions for a 
> productive
> avenue of investigation?
> 
> Thanks very much,
> Will Ware
> 
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