[Python] ctypes: Passing string by reference

With regard to Python 2.5, I wish to implement the following C code in python:

C code:

#include <wtypes.h>

__declspec(dllexport) X_ERROR __stdcall GetAdmSize(INT* piAdmSize, CHAR** chBuf, INT iBufSize);

int iProgSize = 0;
char szProgSize[50];
char* pszProgSize = szProgSize;
error = GetAdmSize(&iProgSize, &pszProgSize, 49);


Python code:

from ctypes import *
c_bool = c_int

x = windll.LoadLibrary("x.dll")
iProgSize = c_int()
szProgSize = create_string_buffer(50)
getAdmSize = x.AdkGetAdmSize
getAdmSize.argtypes = [POINTER(c_int), POINTER(c_char_p), c_int]
status = getAdmSize(byref(iProgSize), byref(szProgSize), 49)


But I'm getting the following exception:

Traceback (most recent call last):
status = getAdmSize(byref(iProgSize), (szProgSize), 49)
ArgumentError: argument 2: <type 'exceptions.TypeError'>: expected LP_c_char_p instance instead of c_char_Array_50


What am I doing wrong?

UPDATE:

I tried:

pointerToStringBuffer = cast(szProgSize, c_char_p)
status = getAdmSize(byref(iProgSize), byref(pointerToStringBuffer), 49)


But this gives me:

Traceback (most recent call last):
status = getAdmSize(byref(iProgSize), byref(pointerToStringBuffer), 49)
WindowsError: exception: access violation reading 0x00000031


As a matter of interest, I get the same error in C if I call this:

error = AdkGetAdmSize((int*)0, (char**)49, 0);


Seems like my arguments are not aligned correctly perhaps

Any suggestions?

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