Calling methods from C/C++ DLL with Python

Question

I do have a tutorial here about calling functions from ac/c++ dll, the example is written here from the official tutorial .

WINUSERAPI int WINAPI
MessageBoxA(
    HWND hWnd,
    LPCSTR lpText,
    LPCSTR lpCaption,
    UINT uType);

Here is the wrapping with ctypes:

>>>
>>> from ctypes import c_int, WINFUNCTYPE, windll
>>> from ctypes.wintypes import HWND, LPCSTR, UINT
>>> prototype = WINFUNCTYPE(c_int, HWND, LPCSTR, LPCSTR, UINT)
>>> paramflags = (1, "hwnd", 0), (1, "text", "Hi"), (1, "caption", None), (1, "flags", 0)
>>> MessageBox = prototype(("MessageBoxA", windll.user32), paramflags)
>>>
The MessageBox foreign function can now be called in these ways:

>>>
>>> MessageBox()
>>> MessageBox(text="Spam, spam, spam")
>>> MessageBox(flags=2, text="foo bar")
>>>
A second example demonstrates output parameters. The win32 GetWindowRect function retrieves the dimensions of a specified window by copying them into RECT structure that the caller has to supply. Here is the C declaration:

WINUSERAPI BOOL WINAPI
GetWindowRect(
     HWND hWnd,
     LPRECT lpRect);
Here is the wrapping with ctypes:

>>>
>>> from ctypes import POINTER, WINFUNCTYPE, windll, WinError
>>> from ctypes.wintypes import BOOL, HWND, RECT
>>> prototype = WINFUNCTYPE(BOOL, HWND, POINTER(RECT))
>>> paramflags = (1, "hwnd"), (2, "lprect")
>>> GetWindowRect = prototype(("GetWindowRect", windll.user32), paramflags)
>>>

This example works when the function is external, however, let's assume I have a reference to an object, and I want to call a function from that object with params, how do I do that?

I did saw the log of all function signatures from 'dumpbin -exports', and I tried using the full name of the function, and still it didn't work.

Any other ideas would be blessed.

Answer 1

Unfortunately, you can not do that easily and in portable way with ctypes .

ctypes is designed to call functions in DLLs with C compatible data types.

Since there is no standard binary interface for C++, you should know how the compiler which generates the DLL, generates the code (ie class layout ... ).

A better solution is to create a new DLL which uses the current DLL and wraps the methods as plain c functions. See boost.python or SWIG for more details.