C Wrapper Function, crashing Python?

**Java and Swing** · Oct 12 '05, 01:15 PM

Re: C Wrapper Function, crashing Python?

update:
if I use C's free(result), free(a) free(b) instead of PyMem_Free...I
only get one successfuly use/call of doStuff.

i.e.
// this works
doStuff(...)

// python crashes here
doStuff(...)

Java and Swing wrote:[color=blue]
> static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> // this will store the result in a Python object
> PyObject *finalResult;
>
> // get arguments from Python
> char *result = 0;
> char *in= 0;
> char *aString = 0;
> char *bString = 0;
> MY_NUM *a;
> MY_NUM *b;
> int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> if (!ok) return 0;
>
> // do work to get a and b
> // count - returns an int; GetVal - returns a char *
> a = GetVal(aString, count(aString, ","));
> b = GetVal(bString, count(bString, ","));
>
> // make function call, which returns a char *
> result = doStuff(in, a, b);
>
> // save result in Python string
> finalResult = PyString_FromSt ring(result);
>
> // free memory
> PyMem_Free(resu lt);
> PyMem_Free(a);
> PyMem_Free(b);
>
> // return the result as a Python string
> return finalResult;
> }
>
> ...from python I can call this function 4 times...works fine. WHen I
> call it for the fifth time python.exe crashes. im thinking some memory
> problem in the wrapper function perhaps...but I am not sure. The
> actually C function, doStuff can be called 5, 6,7...N times without a
> problem
> so i know its gotta be my wrapper.
>
> Any ideas? Thanks![/color]

**Java and Swing** · Oct 12 '05, 01:25 PM

Re: C Wrapper Function, crashing Python?

one more update...

if I remove PyMem_Free and free(...) ...so no memory clean up...I can
still only call doStuff 4 times, the 5th attemp crashes Python.

Java and Swing wrote:[color=blue]
> update:
> if I use C's free(result), free(a) free(b) instead of PyMem_Free...I
> only get one successfuly use/call of doStuff.
>
> i.e.
> // this works
> doStuff(...)
>
> // python crashes here
> doStuff(...)
>
> Java and Swing wrote:[color=green]
> > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> > // this will store the result in a Python object
> > PyObject *finalResult;
> >
> > // get arguments from Python
> > char *result = 0;
> > char *in= 0;
> > char *aString = 0;
> > char *bString = 0;
> > MY_NUM *a;
> > MY_NUM *b;
> > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> > if (!ok) return 0;
> >
> > // do work to get a and b
> > // count - returns an int; GetVal - returns a char *
> > a = GetVal(aString, count(aString, ","));
> > b = GetVal(bString, count(bString, ","));
> >
> > // make function call, which returns a char *
> > result = doStuff(in, a, b);
> >
> > // save result in Python string
> > finalResult = PyString_FromSt ring(result);
> >
> > // free memory
> > PyMem_Free(resu lt);
> > PyMem_Free(a);
> > PyMem_Free(b);
> >
> > // return the result as a Python string
> > return finalResult;
> > }
> >
> > ...from python I can call this function 4 times...works fine. WHen I
> > call it for the fifth time python.exe crashes. im thinking some memory
> > problem in the wrapper function perhaps...but I am not sure. The
> > actually C function, doStuff can be called 5, 6,7...N times without a
> > problem
> > so i know its gotta be my wrapper.
> >
> > Any ideas? Thanks![/color][/color]

**Antoon Pardon** · Oct 12 '05, 01:25 PM

Re: C Wrapper Function, crashing Python?

Op 2005-10-12, Java and Swing schreef <codecraig@gmai l.com>:[color=blue]
> static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> // this will store the result in a Python object
> PyObject *finalResult;
>
> // get arguments from Python
> char *result = 0;
> char *in= 0;
> char *aString = 0;
> char *bString = 0;
> MY_NUM *a;
> MY_NUM *b;
> int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> if (!ok) return 0;
>
> // do work to get a and b
> // count - returns an int; GetVal - returns a char *
> a = GetVal(aString, count(aString, ","));
> b = GetVal(bString, count(bString, ","));
>
> // make function call, which returns a char *
> result = doStuff(in, a, b);
>
> // save result in Python string
> finalResult = PyString_FromSt ring(result);
>
> // free memory
> PyMem_Free(resu lt);
> PyMem_Free(a);
> PyMem_Free(b);
>
> // return the result as a Python string
> return finalResult;
> }
>
> ...from python I can call this function 4 times...works fine. WHen I
> call it for the fifth time python.exe crashes. im thinking some memory
> problem in the wrapper function perhaps...but I am not sure. The
> actually C function, doStuff can be called 5, 6,7...N times without a
> problem
> so i know its gotta be my wrapper.
>
> Any ideas? Thanks![/color]

Well assuming your doStuff is a C function that knows nothing of python.
it might be the PyMem_Free(resu lt).
http://docs.python.org/api/memoryInterface.html says the following:

void PyMem_Free(void *p)
Frees the memory block pointed to by p, which must have been
returned by a previous call to PyMem_Malloc() or PyMem_Realloc() .
Otherwise, or if PyMem_Free(p) has been called before, undefined
behavior occurs. If p is NULL, no operation is performed.

But your result wasn't allocated by a PyMem_Malloc, it was returned
to you by a C function.

--
Antoon Pardon

**Java and Swing** · Oct 12 '05, 01:35 PM

Re: C Wrapper Function, crashing Python?

Antoon,
I just saw that to. I updated the code like so...

static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
// this will store the result in a Python object
PyObject *finalResult;

// get arguments from Python
char *result = 0;
char *in= 0;
char *aString = 0;
char *bString = 0;
MY_NUM *a = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
the array will be 20 long
MY_NUM *b = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
the array will be 20 long
int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
if (!ok) return 0;

// do work to get a and b
// count - returns an int; GetVal - returns a MY_NUM * (a pointer
to a MY_NUM array)
a = GetVal(aString, count(aString, ","));
b = GetVal(bString, count(bString, ","));

// make function call, which returns a char *
result = doStuff(in, a, b);

// save result in Python string
finalResult = PyString_FromSt ring(result);

// free memory
PyMem_Free(a);
PyMem_Free(b);
free(aString);
free(bString);
free(result);

// return the result as a Python string
return finalResult;
}

...as you can see, i malloc'ed memory, and free'd the memory. However,
I still have python crashing (after only 3 successful calls to
doStuff). And yes, doStuff is a plain C function...noth ing related to
Python.

Antoon Pardon wrote:[color=blue]
> Op 2005-10-12, Java and Swing schreef <codecraig@gmai l.com>:[color=green]
> > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> > // this will store the result in a Python object
> > PyObject *finalResult;
> >
> > // get arguments from Python
> > char *result = 0;
> > char *in= 0;
> > char *aString = 0;
> > char *bString = 0;
> > MY_NUM *a;
> > MY_NUM *b;
> > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> > if (!ok) return 0;
> >
> > // do work to get a and b
> > // count - returns an int; GetVal - returns a char *
> > a = GetVal(aString, count(aString, ","));
> > b = GetVal(bString, count(bString, ","));
> >
> > // make function call, which returns a char *
> > result = doStuff(in, a, b);
> >
> > // save result in Python string
> > finalResult = PyString_FromSt ring(result);
> >
> > // free memory
> > PyMem_Free(resu lt);
> > PyMem_Free(a);
> > PyMem_Free(b);
> >
> > // return the result as a Python string
> > return finalResult;
> > }
> >
> > ...from python I can call this function 4 times...works fine. WHen I
> > call it for the fifth time python.exe crashes. im thinking some memory
> > problem in the wrapper function perhaps...but I am not sure. The
> > actually C function, doStuff can be called 5, 6,7...N times without a
> > problem
> > so i know its gotta be my wrapper.
> >
> > Any ideas? Thanks![/color]
>
> Well assuming your doStuff is a C function that knows nothing of python.
> it might be the PyMem_Free(resu lt).
> http://docs.python.org/api/memoryInterface.html says the following:
>
> void PyMem_Free(void *p)
> Frees the memory block pointed to by p, which must have been
> returned by a previous call to PyMem_Malloc() or PyMem_Realloc() .
> Otherwise, or if PyMem_Free(p) has been called before, undefined
> behavior occurs. If p is NULL, no operation is performed.
>
> But your result wasn't allocated by a PyMem_Malloc, it was returned
> to you by a C function.
>
> --
> Antoon Pardon[/color]

**Java and Swing** · Oct 12 '05, 01:45 PM

Re: C Wrapper Function, crashing Python?

Antoon,
I just saw that to. I updated the code like so...

static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
// this will store the result in a Python object
PyObject *finalResult;

// get arguments from Python
char *result = 0;
char *in= 0;
char *aString = 0;
char *bString = 0;
MY_NUM *a = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
the array will be 20 long
MY_NUM *b = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
the array will be 20 long
int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
if (!ok) return 0;

// do work to get a and b
// count - returns an int; GetVal - returns a MY_NUM * (a pointer
to a MY_NUM array)
a = GetVal(aString, count(aString, ","));
b = GetVal(bString, count(bString, ","));

// make function call, which returns a char *
result = doStuff(in, a, b);

// save result in Python string
finalResult = PyString_FromSt ring(result);

// free memory
PyMem_Free(a);
PyMem_Free(b);
free(aString);
free(bString);
free(result);

// return the result as a Python string
return finalResult;
}

...as you can see, i malloc'ed memory, and free'd the memory. However,
I still have python crashing (after only 3 successful calls to
doStuff). And yes, doStuff is a plain C function...noth ing related to
Python.

Antoon Pardon wrote:[color=blue]
> Op 2005-10-12, Java and Swing schreef <codecraig@gmai l.com>:[color=green]
> > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> > // this will store the result in a Python object
> > PyObject *finalResult;
> >
> > // get arguments from Python
> > char *result = 0;
> > char *in= 0;
> > char *aString = 0;
> > char *bString = 0;
> > MY_NUM *a;
> > MY_NUM *b;
> > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> > if (!ok) return 0;
> >
> > // do work to get a and b
> > // count - returns an int; GetVal - returns a char *
> > a = GetVal(aString, count(aString, ","));
> > b = GetVal(bString, count(bString, ","));
> >
> > // make function call, which returns a char *
> > result = doStuff(in, a, b);
> >
> > // save result in Python string
> > finalResult = PyString_FromSt ring(result);
> >
> > // free memory
> > PyMem_Free(resu lt);
> > PyMem_Free(a);
> > PyMem_Free(b);
> >
> > // return the result as a Python string
> > return finalResult;
> > }
> >
> > ...from python I can call this function 4 times...works fine. WHen I
> > call it for the fifth time python.exe crashes. im thinking some memory
> > problem in the wrapper function perhaps...but I am not sure. The
> > actually C function, doStuff can be called 5, 6,7...N times without a
> > problem
> > so i know its gotta be my wrapper.
> >
> > Any ideas? Thanks![/color]
>
> Well assuming your doStuff is a C function that knows nothing of python.
> it might be the PyMem_Free(resu lt).
> http://docs.python.org/api/memoryInterface.html says the following:
>
> void PyMem_Free(void *p)
> Frees the memory block pointed to by p, which must have been
> returned by a previous call to PyMem_Malloc() or PyMem_Realloc() .
> Otherwise, or if PyMem_Free(p) has been called before, undefined
> behavior occurs. If p is NULL, no operation is performed.
>
> But your result wasn't allocated by a PyMem_Malloc, it was returned
> to you by a C function.
>
> --
> Antoon Pardon[/color]

**Java and Swing** · Oct 12 '05, 01:55 PM

Re: C Wrapper Function, crashing Python?

Sorry about the double post...

anyhow, after putting in debug statements I found that it was crashing
when it called, free(result)... .so I removed the free(result).

now it crashes when it gets to, b = GetVal(bString, count(bString,
","));

...any ideas?

Java and Swing wrote:[color=blue]
> Antoon,
> I just saw that to. I updated the code like so...
>
> static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> // this will store the result in a Python object
> PyObject *finalResult;
>
> // get arguments from Python
> char *result = 0;
> char *in= 0;
> char *aString = 0;
> char *bString = 0;
> MY_NUM *a = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
> the array will be 20 long
> MY_NUM *b = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
> the array will be 20 long
> int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> if (!ok) return 0;
>
> // do work to get a and b
> // count - returns an int; GetVal - returns a MY_NUM * (a pointer
> to a MY_NUM array)
> a = GetVal(aString, count(aString, ","));
> b = GetVal(bString, count(bString, ","));
>
> // make function call, which returns a char *
> result = doStuff(in, a, b);
>
> // save result in Python string
> finalResult = PyString_FromSt ring(result);
>
> // free memory
> PyMem_Free(a);
> PyMem_Free(b);
> free(aString);
> free(bString);
> free(result);
>
> // return the result as a Python string
> return finalResult;
> }
>
> ..as you can see, i malloc'ed memory, and free'd the memory. However,
> I still have python crashing (after only 3 successful calls to
> doStuff). And yes, doStuff is a plain C function...noth ing related to
> Python.
>
>
> Antoon Pardon wrote:[color=green]
> > Op 2005-10-12, Java and Swing schreef <codecraig@gmai l.com>:[color=darkred]
> > > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> > > // this will store the result in a Python object
> > > PyObject *finalResult;
> > >
> > > // get arguments from Python
> > > char *result = 0;
> > > char *in= 0;
> > > char *aString = 0;
> > > char *bString = 0;
> > > MY_NUM *a;
> > > MY_NUM *b;
> > > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> > > if (!ok) return 0;
> > >
> > > // do work to get a and b
> > > // count - returns an int; GetVal - returns a char *
> > > a = GetVal(aString, count(aString, ","));
> > > b = GetVal(bString, count(bString, ","));
> > >
> > > // make function call, which returns a char *
> > > result = doStuff(in, a, b);
> > >
> > > // save result in Python string
> > > finalResult = PyString_FromSt ring(result);
> > >
> > > // free memory
> > > PyMem_Free(resu lt);
> > > PyMem_Free(a);
> > > PyMem_Free(b);
> > >
> > > // return the result as a Python string
> > > return finalResult;
> > > }
> > >
> > > ...from python I can call this function 4 times...works fine. WHen I
> > > call it for the fifth time python.exe crashes. im thinking some memory
> > > problem in the wrapper function perhaps...but I am not sure. The
> > > actually C function, doStuff can be called 5, 6,7...N times without a
> > > problem
> > > so i know its gotta be my wrapper.
> > >
> > > Any ideas? Thanks![/color]
> >
> > Well assuming your doStuff is a C function that knows nothing of python.
> > it might be the PyMem_Free(resu lt).
> > http://docs.python.org/api/memoryInterface.html says the following:
> >
> > void PyMem_Free(void *p)
> > Frees the memory block pointed to by p, which must have been
> > returned by a previous call to PyMem_Malloc() or PyMem_Realloc() .
> > Otherwise, or if PyMem_Free(p) has been called before, undefined
> > behavior occurs. If p is NULL, no operation is performed.
> >
> > But your result wasn't allocated by a PyMem_Malloc, it was returned
> > to you by a C function.
> >
> > --
> > Antoon Pardon[/color][/color]

**Java and Swing** · Oct 12 '05, 02:45 PM

Re: C Wrapper Function, crashing Python?

ok, further digging...I found that in the C function GetVal...it is
crashing where I try to malloc some memory. Note, I have no problems
when running this from C..just from Python using my wrapper.

GetVal looks something like..
MY_NUM *GetVal(const char *in, const int x) {
MY_NUM *results, *returnResults;
results = (MY_NUM *) malloc((x * sizeof(MY_NUM) + 1);
returnResults = results;
// ..do more work..
return returnResults;
}

I put in print statements into the C code and found that it is crashing
at the line where I malloc some space for "results".

....any ideas why this is crashing when calling from Python via C
wrapper?

Java and Swing wrote:[color=blue]
> Sorry about the double post...
>
> anyhow, after putting in debug statements I found that it was crashing
> when it called, free(result)... .so I removed the free(result).
>
> now it crashes when it gets to, b = GetVal(bString, count(bString,
> ","));
>
> ..any ideas?
>
> Java and Swing wrote:[color=green]
> > Antoon,
> > I just saw that to. I updated the code like so...
> >
> > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> > // this will store the result in a Python object
> > PyObject *finalResult;
> >
> > // get arguments from Python
> > char *result = 0;
> > char *in= 0;
> > char *aString = 0;
> > char *bString = 0;
> > MY_NUM *a = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
> > the array will be 20 long
> > MY_NUM *b = (MY_NUM *) PyMem_Malloc((2 0 * sizeof(MY_NUM) + 1); //
> > the array will be 20 long
> > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> > if (!ok) return 0;
> >
> > // do work to get a and b
> > // count - returns an int; GetVal - returns a MY_NUM * (a pointer
> > to a MY_NUM array)
> > a = GetVal(aString, count(aString, ","));
> > b = GetVal(bString, count(bString, ","));
> >
> > // make function call, which returns a char *
> > result = doStuff(in, a, b);
> >
> > // save result in Python string
> > finalResult = PyString_FromSt ring(result);
> >
> > // free memory
> > PyMem_Free(a);
> > PyMem_Free(b);
> > free(aString);
> > free(bString);
> > free(result);
> >
> > // return the result as a Python string
> > return finalResult;
> > }
> >
> > ..as you can see, i malloc'ed memory, and free'd the memory. However,
> > I still have python crashing (after only 3 successful calls to
> > doStuff). And yes, doStuff is a plain C function...noth ing related to
> > Python.
> >
> >
> > Antoon Pardon wrote:[color=darkred]
> > > Op 2005-10-12, Java and Swing schreef <codecraig@gmai l.com>:
> > > > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> > > > // this will store the result in a Python object
> > > > PyObject *finalResult;
> > > >
> > > > // get arguments from Python
> > > > char *result = 0;
> > > > char *in= 0;
> > > > char *aString = 0;
> > > > char *bString = 0;
> > > > MY_NUM *a;
> > > > MY_NUM *b;
> > > > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> > > > if (!ok) return 0;
> > > >
> > > > // do work to get a and b
> > > > // count - returns an int; GetVal - returns a char *
> > > > a = GetVal(aString, count(aString, ","));
> > > > b = GetVal(bString, count(bString, ","));
> > > >
> > > > // make function call, which returns a char *
> > > > result = doStuff(in, a, b);
> > > >
> > > > // save result in Python string
> > > > finalResult = PyString_FromSt ring(result);
> > > >
> > > > // free memory
> > > > PyMem_Free(resu lt);
> > > > PyMem_Free(a);
> > > > PyMem_Free(b);
> > > >
> > > > // return the result as a Python string
> > > > return finalResult;
> > > > }
> > > >
> > > > ...from python I can call this function 4 times...works fine. WHen I
> > > > call it for the fifth time python.exe crashes. im thinking some memory
> > > > problem in the wrapper function perhaps...but I am not sure. The
> > > > actually C function, doStuff can be called 5, 6,7...N times without a
> > > > problem
> > > > so i know its gotta be my wrapper.
> > > >
> > > > Any ideas? Thanks!
> > >
> > > Well assuming your doStuff is a C function that knows nothing of python.
> > > it might be the PyMem_Free(resu lt).
> > > http://docs.python.org/api/memoryInterface.html says the following:
> > >
> > > void PyMem_Free(void *p)
> > > Frees the memory block pointed to by p, which must have been
> > > returned by a previous call to PyMem_Malloc() or PyMem_Realloc() .
> > > Otherwise, or if PyMem_Free(p) has been called before, undefined
> > > behavior occurs. If p is NULL, no operation is performed.
> > >
> > > But your result wasn't allocated by a PyMem_Malloc, it was returned
> > > to you by a C function.
> > >
> > > --
> > > Antoon Pardon[/color][/color][/color]

**Bernhard Herzog** · Oct 12 '05, 04:15 PM

Re: C Wrapper Function, crashing Python?

"Java and Swing" <codecraig@gmai l.com> writes:
[color=blue]
> static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {[/color]
[...][color=blue]
> char *aString = 0;
> char *bString = 0;[/color]
[...][color=blue]
> int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);[/color]
[...][color=blue]
> free(aString);
> free(bString);[/color]

aString and bString are pointers to memory managed by the strings in
your args tuple. You must not free them! The memory is automatically
managed by Python.

Bernhard

--
Intevation GmbH http://intevation.de/
Skencil http://skencil.org/
Thuban http://thuban.intevation.org/

**Java and Swing** · Oct 12 '05, 04:25 PM

Re: C Wrapper Function, crashing Python?

thanks for the tip, however even when I do not free aString or bString,
i'm still crashing at the malloc in the c function, not the wrapper.

Bernhard Herzog wrote:[color=blue]
> "Java and Swing" <codecraig@gmai l.com> writes:
>[color=green]
> > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {[/color]
> [...][color=green]
> > char *aString = 0;
> > char *bString = 0;[/color]
> [...][color=green]
> > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);[/color]
> [...][color=green]
> > free(aString);
> > free(bString);[/color]
>
> aString and bString are pointers to memory managed by the strings in
> your args tuple. You must not free them! The memory is automatically
> managed by Python.
>
> Bernhard
>
> --
> Intevation GmbH http://intevation.de/
> Skencil http://skencil.org/
> Thuban http://thuban.intevation.org/[/color]

**Bernhard Herzog** · Oct 12 '05, 04:35 PM

Re: C Wrapper Function, crashing Python?

"Java and Swing" <codecraig@gmai l.com> writes:
[color=blue]
> thanks for the tip, however even when I do not free aString or bString,
> i'm still crashing at the malloc in the c function, not the wrapper.[/color]

Do you have any more places where you use free incorrectly? In my
experience, calling free with invalid values can corrupt the data
structures used by the memory allocator in such a way that subsequent
malloc calls crash.

Bernhard

--
Intevation GmbH http://intevation.de/
Skencil http://skencil.org/
Thuban http://thuban.intevation.org/

**Java and Swing** · Oct 12 '05, 04:45 PM

Re: C Wrapper Function, crashing Python?

As far as my C Wrapper functions are concerned...I no longer have the
need for free(...). I do use PyMem_Free, for structures I allocated by
using PyMem_New(...).

In my C code I do have things such as...

char *foo(const char *in) {
char *tmp;
tmp = (char *) malloc((strlen( in) * sizeof(char)) + 1);
strcpy(tmp, in);
...
...
free(tmp);
return someValue;
}

Is that appropriate? I was under the impression that when you malloc
memory, you free it when done.

I also have things like...

char *bar(char *in) {
char *results, *finalResults;
results = (char *) malloc(...);
finalResults = results;

while (...) { *results++ = some_val; }

return finalResults;
}

....is that correct?

As I mentioned earlier, when I run these functions from C I have no
troubles...I can run them 5, 10, 15 times, etc. From Python, using my
wrapper function is when I have trouble.

Thanks in advance.

Bernhard Herzog wrote:[color=blue]
> "Java and Swing" <codecraig@gmai l.com> writes:
>[color=green]
> > thanks for the tip, however even when I do not free aString or bString,
> > i'm still crashing at the malloc in the c function, not the wrapper.[/color]
>
> Do you have any more places where you use free incorrectly? In my
> experience, calling free with invalid values can corrupt the data
> structures used by the memory allocator in such a way that subsequent
> malloc calls crash.
>
> Bernhard
>
> --
> Intevation GmbH http://intevation.de/
> Skencil http://skencil.org/
> Thuban http://thuban.intevation.org/[/color]

**Bernhard Herzog** · Oct 12 '05, 04:55 PM

Re: C Wrapper Function, crashing Python?

"Java and Swing" <codecraig@gmai l.com> writes:
[color=blue]
> char *foo(const char *in) {
> char *tmp;
> tmp = (char *) malloc((strlen( in) * sizeof(char)) + 1);
> strcpy(tmp, in);
> ...
> ...
> free(tmp);
> return someValue;
> }
>
> Is that appropriate? I was under the impression that when you malloc
> memory, you free it when done.[/color]

Looks fine. I hope someValue does not point somewhere into the tmp
buffer, though.
[color=blue]
> I also have things like...
>
> char *bar(char *in) {
> char *results, *finalResults;
> results = (char *) malloc(...);
> finalResults = results;
>
> while (...) { *results++ = some_val; }
>
> return finalResults;
> }[/color]

Seems OK, too, assuming the results buffer is big enough.

Bernhard

--
Intevation GmbH http://intevation.de/
Skencil http://skencil.org/
Thuban http://thuban.intevation.org/

**Java and Swing** · Oct 12 '05, 05:05 PM

Re: C Wrapper Function, crashing Python?

Bernhard Herzog wrote:[color=blue]
> "Java and Swing" <codecraig@gmai l.com> writes:
>[color=green]
> > char *foo(const char *in) {
> > char *tmp;
> > tmp = (char *) malloc((strlen( in) * sizeof(char)) + 1);
> > strcpy(tmp, in);
> > ...
> > ...
> > free(tmp);
> > return someValue;
> > }
> >
> > Is that appropriate? I was under the impression that when you malloc
> > memory, you free it when done.[/color]
>
> Looks fine. I hope someValue does not point somewhere into the tmp
> buffer, though.[/color]

someValue doesn't.
[color=blue]
>[color=green]
> > I also have things like...
> >
> > char *bar(char *in) {
> > char *results, *finalResults;
> > results = (char *) malloc(...);
> > finalResults = results;
> >
> > while (...) { *results++ = some_val; }
> >
> > return finalResults;
> > }[/color]
>
> Seems OK, too, assuming the results buffer is big enough.[/color]

results = (char *) malloc((sizeof( char) * strlen(in) + 1);
..should be big enough. At any rate, it works four times in a row
before it fails.

I wonder what else or how else to solve this. Why is malloc'ing
the memory crashing it!?

**Tony Nelson** · Oct 15 '05, 05:05 AM

Re: C Wrapper Function, crashing Python?

In article <1129122788.882 046.4270@o13g20 00cwo.googlegro ups.com>,
"Java and Swing" <codecraig@gmai l.com> wrote:
[color=blue]
> one more update...
>
> if I remove PyMem_Free and free(...) ...so no memory clean up...I can
> still only call doStuff 4 times, the 5th attemp crashes Python.
>
> Java and Swing wrote:[color=green]
> > update:
> > if I use C's free(result), free(a) free(b) instead of PyMem_Free...I
> > only get one successfuly use/call of doStuff.
> >
> > i.e.
> > // this works
> > doStuff(...)
> >
> > // python crashes here
> > doStuff(...)
> >
> > Java and Swing wrote:[color=darkred]
> > > static PyObject *wrap_doStuff(P yObject *self, PyObject *args) {
> > > // this will store the result in a Python object
> > > PyObject *finalResult;
> > >
> > > // get arguments from Python
> > > char *result = 0;
> > > char *in= 0;
> > > char *aString = 0;
> > > char *bString = 0;
> > > MY_NUM *a;
> > > MY_NUM *b;
> > > int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
> > > if (!ok) return 0;
> > >
> > > // do work to get a and b
> > > // count - returns an int; GetVal - returns a char *
> > > a = GetVal(aString, count(aString, ","));
> > > b = GetVal(bString, count(bString, ","));
> > >
> > > // make function call, which returns a char *
> > > result = doStuff(in, a, b);
> > >
> > > // save result in Python string
> > > finalResult = PyString_FromSt ring(result);
> > >
> > > // free memory
> > > PyMem_Free(resu lt);
> > > PyMem_Free(a);
> > > PyMem_Free(b);
> > >
> > > // return the result as a Python string
> > > return finalResult;
> > > }
> > >
> > > ...from python I can call this function 4 times...works fine. WHen I
> > > call it for the fifth time python.exe crashes. im thinking some memory
> > > problem in the wrapper function perhaps...but I am not sure. The
> > > actually C function, doStuff can be called 5, 6,7...N times without a
> > > problem
> > > so i know its gotta be my wrapper.
> > >
> > > Any ideas? Thanks![/color][/color]
>[/color]

I think your wrapper should look something like:

static PyObject *wrap_doStuff(P yObject *self, PyObject *args)
{
// this will store the result in a Python object
PyObject *finalResult;

// get arguments from Python
char *result = 0;
char *in= 0;
char *aString = 0;
char *bString = 0;
MY_NUM *a;
MY_NUM *b;

int ok = PyArg_ParseTupl e(args, "sss", &in, &aString, &bString);
if (!ok) return 0;

// do work to get a and b
// count - returns an int; GetVal - returns a char *
a = GetVal(aString, count(aString, ","));
b = GetVal(bString, count(bString, ","));

// make function call, which returns a char *
result = doStuff(in, a, b);

// save result in Python string
finalResult = PyString_FromSt ring(result);

// free memory
free(result);
free(a);
free(b);

// return the result as a Python string
return finalResult;
}

You must match malloc() with free(), and PyMem_Malloc() with
PyMem_Free(). Malloc() and free() usually crash /after/ the call that
did the damage. You may wish to avail yourself of your platform's
malloc debugging facilities.

Note that I don't do this stuff in C, I do it in pyrex, and I'm new to
it anyway, so there may still be something wrong. Unless you are
determined to learn how to do this in C, I think you should switch to
pyrex.
_______________ _______________ _______________ _______________ ____________
TonyN.:' *firstname*nlsn ews@georgea*las tname*.com
' <http://www.georgeanels on.com/>

C Wrapper Function, crashing Python?

C Wrapper Function, crashing Python?

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