I have a C function in a dll file defined as follows:

myFunction(const int a, long b, void * data, unsigned int * c, unsigned int * d, unsigned long * timestamp)

Parameters:

[in]: a
[in]: b
[out]: data, which is a pointer to a buffer that is maximum of 8 bytes
[out]: c, points to a buffer that receives data message length
[out]: d, pointer to a buffer which receives a message flag
[out]: timestamp, pointer to a buffer which receives message timestamp

My python code is as follows:

import ctypes

dllhandle = ctypes.WinDLL("dllFile.dll")

a = 1
b = 1738
data = ctypes.c_void_p*8
c = 0
d = 0
timestamp = 0

dllhandle.myFunction(a, b, data, c, d, timestamp)

When I run my python code, I get the following error:

ctypes.ArgumentError: argument 3: <type 'exceptions.TypeError'>: Don't know how to convert parameter 3.

I figured this has to do with how I am creating my data buffer pointer array. What is the proper way of creating the data buffer?

You should use an array of chars to pass your data. I have written this script that could help you:

"""
extern "C" void your_func(void* buffer, int size);
"""
# For Python 2.7
import ctypes

BUFFER_SIZE = 256

# Importing dll
dll = ctypes.CDLL("dllFile.dll")

# Defining C-arguments and output
buffer_c_type = lambda chars: (ctypes.c_char * BUFFER_SIZE)(*map(ctypes.c_char, chars))
size_c_type = ctypes.c_int
restype = None # None is for 'void' as the result of your function in C

# Creating C-arguments having Python variables 'buffer' and 'BUFFER_SIZE'
buffer = "qwdeasdvwergb"
c_buffer = buffer_c_type(buffer)
c_size = size_c_type(BUFFER_SIZE)

# Extracting your_func from dll and setting the type of returning value
your_func = dll["your_func"]
your_func.restype = restype

# Running your_func
your_func(c_buffer, c_size)