[capi-sig] Extension Problem

[Anthony Tuininga]

I suspect the problem is the following:

double *min_eps;

if (!PyArg_ParseTuple(args, "d", &min_eps))
    return NULL;

That should be

double min_eps;

as Python is expecting a double, not a pointer to a double! And since
the difference is about 4 bytes, that would explain the segfault. :-)

Anthony

On 8/14/07, Ali Alhakim <alika at spray.se> wrote:
> Hello!
>
> I'm quite new to Python and definitely a beginner in implementing Python
> extensions in C/C++. I've followed the structure given in the formal Python
> documentation to write the following code block:
> ===========
> //cmatmod.c
>
> #include
>
> static unsigned int eigenvect_calc(double *min_eps)
> {
>  return 5;
> }
>
> static PyObject *cmat_eigv(PyObject *self, PyObject *args)
> {
>  double *min_eps;
>  unsigned int m;
>  if(!PyArg_ParseTuple(args, "d", &min_eps))
>   return NULL;
>  m=eigenvect_calc(min_eps);
>  return Py_BuildValue("I", m);
>  }
> static PyMethodDef cmat_methods[]=
> {
>  { "eigenvect", cmat_eigv, METH_VARARGS, "Comment"},{NULL, NULL, 0, NULL}
>  };
>
> void initcmat(void)
> {
>   (void) Py_InitModule("cmat", cmat_methods);
>  }
>
> ===========
>
> I have succeeded to build and install this extension using disutils package
> in the setup.py file below:
> ===========
> from distutils.core import setup
> from distutils.extension import Extension
> setup(name='eigenvect',
>       version='1.0',
>       ext_modules=[Extension('cmat', ['cmatmod.c'])],
>       )
>
> ==========
> But when I try to call eigenvect(3.0) from Python I would receive a core
> dump:
> ==========
>
>  6 [main] python 2336 _cygtls::handle_exceptions: Error while dumping state
>  (probably corrupted stack)
> Segmentation fault (core dumped)
>
> ==========
> My question is what is wrong with the extension code above? Is it something
> with reference counting?
> I don't know which method is suitable for debugging extension codes. I've
> tried gdb but I didn't understand the debug information:
> ==========
>
> (gdb) >>> eigenvect(4.0)
>
> Program received signal SIGSEGV, Segmentation fault.
> ---Type  to continue, or q  to quit---
> 0x6abb248e in libpython2!PyEval_EvalFrameEx () from
> /usr/bin/libpython2.5dll
> (gdb)
>
> ==========
> /best regards
>
>
>
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>
> Gå in och titta på nätets roligaste filmer just nu eller ladda upp ditt eget bidrag på Spray Crazy. http://crazy.spray.se/
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