ctypes FAQ - frequently asked questions

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  Windows topics

    How do I pass a win32all 'PyHandle' to a dll function?

       'win32all' functions often return a 'PyHandle' object, for
       example the 'CreateFile' function.  'ctypes' has it's own
       protocol to convert Python objects into C parameters when it
       calls functions loaded from a dll, so it does not know how to
       pass the 'PyHandle' object to the C function.

       'PyHandle' objects have a '.handle' attribute which is an
       integer, and this can be passed to a function by 'ctypes' ::

           h = win32file.CreateFile(....)
	   windll.kernel32.DeviceIoControl(h.handle, ...)

       Another possibility is to convert the 'PyHandle' object into an
       integer by writing the call in this way::

           h = win32file.CreateFile(....)
	   windll.kernel32.DeviceIoControl(int(h), ...)

    How can I call functions in a dll written in Delphi?

       Delphi uses the 'PASCAL' calling convention as default, and
       this expects the parameters in reverse order.  Write the
       arguments in reverse order in the call, and it should work when
       using the __stdcall calling convention (load the Delphi dll
       with 'windll').

  General topics

    How can I access a value (an integer, a pointer) in a shared library?

       **New in 0.6.1**: 'ctypes' types now have a '.in_dll' class
       method, which accepts a dll/shared library instance and a
       symbol name as parameters. See the tutorial for details.

    How can I load a dll named 'gpib-32.dll'?

       'ctypes' loads dlls by retrieving them as attributes from
       'windll' or 'cdll', like 'windll.gdi32' which loads
       'gdi32.dll'.  This approach cannot work when the filename
       contains characters not allowed in Python identifiers, or when
       the dll is not on the default Windows search path.  In these
       cases you should call the 'CDLL' or 'WinDLL' classes directly
       with the filename::

           gpib32 = CDLL("c:\\gpib\\gpib-32.dll")

    How can I call functions written in "C++" ?

       Jimmy Retzlaff explains how the C++ compiler mangles function names
       and how it can be avoided in this
       "*post*":http://sourceforge.net/mailarchive/forum.php?thread_id=1604647&forum_id=24606
       to the ctypes-users mailing list.


    How can I help to improve this FAQ?

       Send new questions, better answers, or other comments to the
       "ctypes-users":mailto:ctypes-users@lists.sourceforge.net
       mailing list.