Calling the C++ function in python using ctypes

Question

I have C++ code which has a function which takes, three arguments

1. Pointer argument
2. LPWSTR argument
3. (LPWSTR variable)reference as argument Below is the C++ Code syntax

HRESULT WINAPIV GIDItem (Address* pa, LPWSTR cmdvalue, LPWSTR* string_value)

I am able to load the dll in Ctypes

 import ctypes
 uDl = ctypes.CDLL(r"test1")
 uDl_function=uDl.CAIA # we are creating function pointer
 pa=uDl_function('something')
 uD = ctypes.CDLL(r"test.dll")
 uD_function =uD.GIDItem # we are creating function pointer
 string_value= ctypes.c_wchar_p()
 cmdvalue=ctypes.c_wchar_p("CM")
 dI=uD_function(ctypes.POINTER(pa),cmdvalue,ctypes.byref(string_value))

I am getting below error,

dI=uD_function(ctypes.POINTER(pa),cmdvalue,ctypes.byref(string_value))
TypeError: must be a ctypes type

I was just looking some article about that DLL, in C++ the Dll been called like below

fpGIDItem (pA, L"CMD", &cD)

When you look to the above code "CMD" is the cmdvalue and string value is sent with &cD

Please help me over this

• gnodab: I can't tell where pa is declared. Am I missing something?
• Sreevathsabr: I just updated the code for pa.Thanks for looking to this
• gnodab: You probably need to include a minimal working example. In the meantime see if this helps.
• Sreevathsabr: I don't have c++ dll code, i just know the input type, function name, and return
• Mark Tolonen: POINTER is a type and you need an instance of a type. Since the first parameter is Address* is can probably be just pa if that is what is returned from the first function. byref(string_value) is actually passing a wchar_t** which isn't what you want either. Just pass string_value. Update your question with the full C prototypes of both functions if you want a better answer.

Answer 1

ctypes.POINTER(pa) is a type instead of an instance which is why it is giving the error you see.

If you create a working example of the use in C, it would be easier to identify how to write it in Python, but I'll take a stab at it.

Set .argtypes and restype on the function correctly so ctypes will type check for you.

Something like the following should work.

from ctypes import *
dll = CDLL(r'test1')
dll.CAIA.argtypes = c_wchar_p,
dll.CAIA.restype = c_void_p # generic void* should work.
dll2 = ctypes.CDLL(r'test.dll')
dll2.GIDItem.argtypes = c_void_p,c_wchar_p,POINTER(c_wchar_p)
dll2.GIDItem.restype = c_long
pa = dll.CAIA('something')
string_value = c_wchar_p()
result = dll2.GIDItem(pa,'CM',byref(string_value))

• Sreevathsabr: Thanks, a lot Mark! It worked well and fine.. It's getting the expected result. But I have the only thing if you how to enable the logs so that that I can log any error when we have any error when we called function from ctypes.