Question

given the following code:

import ctypes     ip='192.168.1.1' thisdll = ctypes.cdll['aDLL'] thisdll.functionThatExpectsAnIP(ip) 

how can I correctly pack this for a DLL that expects it as a c_ulong datatype?

I’ve tried using:

ip_netFrmt = socket.inet_aton(ip) ip_netFrmt_c = ctypes.c_ulong(ip_netFrmt) 

however, the c_ulong() method returns an error because it needs an integer.

is there a way to use struct.pack to accomplish this?

Answer 1

The inet_aton returns a string of bytes. This used to be the lingua franca for C-language interfaces.

Here’s how to unpack those bytes into a more useful value.

>>> import socket >>> packed_n= socket.inet_aton('128.0.0.1') >>> import struct >>> struct.unpack( '!L', packed_n ) (2147483649L,) >>> hex(_[0]) '0x80000001L' 

This unpacked value can be used with ctypes. The hex thing is just to show you that the unpacked value looks a lot like an IP address.