How to pass file pointer in dll routines using ctypes in python

Question

I'm accessing one function from dll which need file pointer (char *filename). How can I pass it through python?

handle = cdll.dsp

p = open("signal.txt", "r")

handle.filter(p)

Answer 1

A file pointer is FILE * . But you mentioned you need char *filename , which is a char pointer (ie a null-terminated string). I'm going to assume the C function has a prototype void filter(char *filename) .

First you must define the function argument types and the return type :

import ctypes
filter = ctypes.cdll.dsp.filter
filter.argtypes = (ctypes.c_char_p,)
filter.restype = None  # Or whatever type it returns.

Then you call it:

filter("signal.txt")

By the way, you tagged your question as Python 2.7, but nowadays you should move on to Python 3, unless you have a really good reason to stay at the older version.