Change value in shared library with ctypes

Question

I have the following lib.c :

#include <stdio.h>

double var = 4;

double* fun() {
    printf("%zd %f\n", &var, var);
    return &var;
}

and the following main.py :

import ctypes
lib = ctypes.cdll.LoadLibrary('lib.so')
fun = lib.fun
fun.restype = ctypes.POINTER(ctypes.c_double)

print ctypes.addressof(fun().contents)

How can I, inside the .py , change the double stored at the address of fun().contents , eg, set var to 10.2 ?

Answer 1

The following will change the value:

import ctypes
lib = ctypes.cdll.LoadLibrary('x')
fun = lib.fun
fun.restype = ctypes.POINTER(ctypes.c_double)
v = fun()
v.contents.value = 2.0
v = fun()

Output (note for C function I used %p instead of %zd ):

000007FEFAC14000 4.000000
000007FEFAC14000 2.000000