Python callback

Working example for python callback

############## main.c ##############
#include <stdint.h>
#include <stdio.h>

struct mes_t
{
    uint32_t field1;
    uint32_t field2;
    void* data;
};

typedef int function_callback(struct mes_t* message );

function_callback* my_callback;

int function_one(function_callback fcb){
	//Set to a global variable for later use
	my_callback = fcb;

	//Declare object in stack
	struct mes_t mes;
	mes.field1 = 132;
	mes.field2 = 264;
	mes.data = NULL;

	//Pass pointer of object in stack, and print the return value
	printf("Got from python: %d\n", my_callback( &mes ) );
}

############ main.py ################
import ctypes

testlib = ctypes.CDLL('./testlib.so')

#Declare the data structure
class mes_t(ctypes.Structure):
    _fields_ = (
        ('field1', ctypes.c_uint32),
        ('field2', ctypes.c_uint32),
        ('data', ctypes.c_void_p))

#Declare the callback type, since that is not stored in the library
callback_type = ctypes.CFUNCTYPE(ctypes.c_int, ctypes.POINTER(mes_t) )

def the_callback(mes_p):
    #dereference the pointer
    my_mes = mes_p[0]

    print "I got a mes_t object! mes.field1=%r, mes.field2=%r, mes.data=%r" \
          % (my_mes.field1, my_mes.field2, my_mes.data)

    #Return some random value
    return 999

#Let the library know about the callback function by calling "function_one"
result = testlib.function_one(callback_type(the_callback) )

#########################
gcc -shared -o testlib.so -fPIC main.c
python main.py