ctypes and pointers

Diez B. Roggisch

Hi,

I'm working under mac os x with the OpenCV-library that I load via ctypes.

From a ObjectiveC-methodcall I get an integer, that "really" is a
pointer to an IplImage-structure.

I've got a function that takes such a pointer. But I don't find a way to
pass it to that very function.

These are the relevant parts of my code:

cvImage = self._f.cvImage ()
print "Address of IplImage: %x" % cvImage
cvImage = c_void_p(cvImag e)
print cvImage
cvImage2 = macopencv.cvClo neImage(cvImage )

The output is

2007-04-14 19:22:53.910 SequenceGrabber Test[5320] Returning IplImage at
Address of IplImage: e860c60
e860c60
c_void_p(243666 016)
2007-04-14 19:22:53.915 SequenceGrabber Test[5320] Exception raised
during posting of notification. Ignored. exception:
exceptions.Valu eError: depythonifying 'pointer', got 'int'
The first line is actually from the ObjectivC-method, a log-statement.

As one can see, the pointer is passed back as integer.

But then I'm stuck.

Any suggestions would be appreciated!

diez

Apr 14 '07 #1

Subscribe Reply

3412

per9000

[This might be a double posting, if it isn't my previous post was
lost]

Look up "restype" in the ctypes library - it sets the return type from
a function. You may want to set it to c_void_p of something similar,
instead of the default int.

I made a similar discovery in my blog -
http://www.pererikstrandberg.se/blog...thonCansiCombo
..

This example loads the function find_root from the dll
root_find_lib.d ll into the variable "find". the restype of find is
then set to a c_double. This means that the item returned from C is a
C_double and not the default int.
root_find_lib = windll.LoadLibr ary("root_find_ lib.dll")
find = root_find_lib.f ind_root
find.restype = c_double
You may already know this but 243666016 == 0E860C60 in different
bases.

HTH,
Per

[:)]-|--<

--

Per Erik Strandberg
..NET Architect - Optimization
Tomlab Optimization Inc.
http://tomopt.com/tomnet/

On 14 Apr, 19:25, "Diez B. Roggisch" <d...@nospam.we b.dewrote:

Hi,

I'm working under mac os x with the OpenCV-library that I load viactypes.

From a ObjectiveC-methodcall I get an integer, that "really" is a
pointer to an IplImage-structure.

I've got a function that takes such a pointer. But I don't find a way to
pass it to that very function.

These are the relevant parts of my code:

cvImage = self._f.cvImage ()
print "Address of IplImage: %x" % cvImage
cvImage = c_void_p(cvImag e)
print cvImage
cvImage2 = macopencv.cvClo neImage(cvImage )

The output is

2007-04-14 19:22:53.910 SequenceGrabber Test[5320] Returning IplImage at
Address of IplImage: e860c60
e860c60
c_void_p(243666 016)
2007-04-14 19:22:53.915 SequenceGrabber Test[5320] Exception raised
during posting of notification. Ignored. exception:
exceptions.Valu eError: depythonifying 'pointer', got 'int'

The first line is actually from the ObjectivC-method, a log-statement.

As one can see, the pointer is passed back as integer.

But then I'm stuck.

Any suggestions would be appreciated!

diez

Apr 16 '07 #2

Diez B. Roggisch

per9000 wrote:

[This might be a double posting, if it isn't my previous post was
lost]

Look up "restype" in the ctypes library - it sets the return type from
a function. You may want to set it to c_void_p of something similar,
instead of the default int.

I made a similar discovery in my blog -
http://www.pererikstrandberg.se/blog...thonCansiCombo
.

This example loads the function find_root from the dll
root_find_lib.d ll into the variable "find". the restype of find is
then set to a c_double. This means that the item returned from C is a
C_double and not the default int.
root_find_lib = windll.LoadLibr ary("root_find_ lib.dll")
find = root_find_lib.f ind_root
find.restype = c_double

I found the solution to be

X.from_address( address)

where X is some ctypes.Structur e

Diez

Apr 16 '07 #3

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