Python ctypes and not enough arguments (4 bytes missing)

Question

The function i'm trying to call is:

void FormatError (HRESULT hrError,PCHAR pszText);

from a custom dll using windll.

c_p = c_char_p()
windll.thedll.FormatError(errcode, c_p)

Results in:

ValueError: Procedure probably called with not enough arguments (4 bytes missing)

Using cdll instead increases the bytes missing counter to 12. errcode above is the errercode returned from another function out of the same dll. How do I get the call right?

Answer 1

Have you tried to use the ctypes.HRESULT?

Answer 2

At the very least, you'll get more descriptive errors if you properly set up the argtypes and the restype.

Try doing it this way:

windll.thedll.FormatError.argtypes = [ctypes.HRESULT, ctypes.c_char_p]
windll.thedll.FormatError.restype  = None

There's also a very good chance you are using the wrong calling convention -- check out the Calling Functions section and the Loading Libraries section for details on how to use a different calling convention.

Answer 3

Actually I think you want to use FormatError as provided by ctypes

http://docs.python.org/library/ctypes.html#ctypes.FormatError

ctypes.FormatError([code])

Windows only: Returns a textual description of the error code. If no error code is specified, the last error code is used by calling the Windows api function GetLastError.