ctypes struct containing arrays

Question

I\'m trying to use ctypes. I\'m interested in manipulating C structs containing arrays. Consider the following my_library.c

#includ         


        

Answer 1

There were 2 problems with the code (as I stated in the comment):

1. print_array_struct.argtype - which is incorrect
2. In C the arrays are double based, while in Python they are ctypes.c_int (int) based

For more details, check [Python 3.Docs]: ctypes - A foreign function library for Python.
I modified your Python code, to correct the above mistakes (and some other minor stuff).

code00.py:

#!/usr/bin/env python3

import sys
import ctypes


DLL_NAME = "./my_so_object.so"

DOUBLE_10 = ctypes.c_double * 10

class ArrayStruct(ctypes.Structure):
    _fields_ = [
        ("first_array", DOUBLE_10),
        ("second_array", DOUBLE_10),
    ]


def main():
    dll_handle = ctypes.CDLL(DLL_NAME)
    print_array_struct_func = dll_handle.print_array_struct
    print_array_struct_func.argtypes = [ArrayStruct]
    print_array_struct_func.restype = None

    x1 = DOUBLE_10()
    x2 = DOUBLE_10()
    x1[:] = range(1, 11)
    x2[:] = range(11, 21)
    print([item for item in x1])
    print([item for item in x2])
    arg = ArrayStruct(x1, x2)
    print_array_struct_func(arg)


if __name__ == "__main__":
    print("Python {:s} on {:s}\n".format(sys.version, sys.platform))
    main()

Output:

[cfati@cfati-ubtu16x64-0:~/Work/Dev/StackOverflow/q050447199]> python3 code00.py
Python 3.5.2 (default, Nov 23 2017, 16:37:01)
[GCC 5.4.0 20160609] on linux

[1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0]
[11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0]
1.000000
2.000000
3.000000
4.000000
5.000000
6.000000
7.000000
8.000000
9.000000
10.000000

---

Update #0

Error #1. is a "duplicate" of (newer) [SO]: C function called from Python via ctypes returns incorrect value (@CristiFati's answer).