import json
from ctypes import Structure, c_int
from ctypes_json import CDataJSONEncoder

class Data(Structure):
    _fields_ = [
        ('a', c_int),
        ('b', c_int),
        ('c', c_int),
    ]

data = Data()

data.a = 10
data.b = 20
data.c = 30

json.dumps(data, cls=CDataJSONEncoder)