Wrapping simple c++ example with ctypes; segmentation fault

Question

I extended the example provided in this answer by adding a private member variable, and printing it in the bar() function:

#include 

        

Answer 1

If you're using 64-bit Python, you need to define the restype and argtypes. Otherwise ctypes defaults to casting the values to a 32-bit C int.

from ctypes import *

lib = CDLL('./libfoo.so')

lib.Foo_new.argtypes = []
lib.Foo_new.restype = c_void_p

lib.Foo_bar.argtypes = [c_void_p]
lib.Foo_bar.restype = None

Here are source links for 2.7.5, Modules/_ctypes/callproc.c:

• ConvParam (Lines 645-663)
• GetResult (Lines 914-915)

For 64-bit Windows a C long is 32-bit, but it's 64-bit on most other 64-bit platforms. By forcing int the result is at least consistent.