[C++-sig] Strange Behavior w/File Pointers

[Michael Wieher]

mYmodule.cpp
---------------------------

istream globalFile;
struct dataStruct {
   int a;
   int b;
   short c;
} __attribute__(align(2));

PyObject *
mYmodule_setFile() {
    --parseTuple--
    globalFile.open(pathToFile,ios::in|ios::binary);
}

PyObject *
mYmodule_getNBytesAtATime() {
  --parseTuple--
  int N;  //the size of a dataStruct
  globalFile.read((char*)&dataStruct,N);
  Py_BuildValue('ii',dataStruct->a, dataStruct->b);
}

==============
Given the above rough pseudocode, I find that each time my Python module
calls myModule.getNBytesAtATime() the file-pointer shifts strangely.  Most
of the time it shifts N bytes.  But, sometimes, on the same points but with
no definable reason that I can see, it shifts N*x bytes, where x is some
integer.

I've fixed the problem by manually resetting the file-pointer on re-entry to
getNBytesAtATime, so the code works, but if anyone can shed some light on
this little quirk, I'd be interested.

-Mike
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