[Swig-user] How to receive a FILE* from Python under MinGW?

John Pye john.pye at student.unsw.edu.au
Wed Mar 21 04:46:03 CET 2007

Hi Carl

I'm not sure that your snippet really solves my problem. As far as I can
see from, you're just passing a filename instead of a file pointer,
right? And then you're using the Python fopen-equivalent
(PyFile_FromString) This is not an option for me, as I want to pass the
FILE* from Python and all the way into into a existing shared-library
code. I can't change the latter; it must work ok with standard fprintf
(etc) functions.

If I've missed something, perhaps you could clarify a little bit more on
how it is that you're overcoming the FILE* problem?


See also


Carl Douglas wrote:
> Hi John,
> I had exactly this problem... use the PyFile_AsFile function.  Below
> is a code snippet from my project:
>         // Thank you:  http://www.ragestorm.net/tutorial?id=21#8
>         PyObject* PyFileObject = PyFile_FromString(ofn.lpstrFile, "r");
>         if (PyFileObject == NULL)
>         {
>             PyErr_Print();
>             PyErr_Clear();
>             return false;
>         }
>         // Because microsoft C runtimes are not binary compatible, we
> can't
>         // just call fopen to get a FILE * and pass that FILE * to
> another application
>         // or library (Python25.dll in this case) that uses a
> different version
>         // of the C runtime that this DLL uses. Using PyFile_AsFile is a
> work-around...
>         if (PyRun_SimpleFile(PyFile_AsFile(PyFileObject),
> ofn.lpstrFile) == -1)
>         {
>             PyErr_Print();
>             PyErr_Clear();
>         }
>         Py_DECREF(PyFileObject);
> For the full source of my SWIG/Python project, poke around here:
> http://l3dtpython.googlecode.com/svn/trunk/cdPython/
> Hope that helps.
> On 3/21/07, John Pye <john.pye at student.unsw.edu.au> wrote:
>> Hi all
>> There is fairly well-known problem on MinGW with passing FILE pointers
>> to Python. The problem seems to be that Python depends on a different
>> version of msvcrt*.dll to that which MinGW depends on, and these
>> different C runtimes provide different FILE implementations.
>> The upshot of that seems to be that file objects created in Python via
>> the 'file(...)' command can't safely be used in a SWIG module. It can be
>> done perfectly (using SWIG typemap and PyFile_AsFile) on Linux but it
>> fails with a segfault on Windows.
>> What is the best possible workaround for this? Surely someone must have
>> found a satisfactory solution to this problem?
>> Cheeers
>> JP 

John Pye
Department of Mechanical and Manufacturing Engineering
University of New South Wales, Sydney, Australia

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