Passing a set of NumPy arrays into C function for input and output

Question

Let\'s assume we have a C function that takes a set of one or more input arrays, processes them, and writes its output into a set of output arrays. The signature looks as follow

Answer 1

To do this specifically with Numpy arrays, you could use:

import numpy as np
import ctypes

count = 5
size = 1000

#create some arrays
arrays = [np.arange(size,dtype="float32") for ii in range(count)] 

#get ctypes handles
ctypes_arrays = [np.ctypeslib.as_ctypes(array) for array in arrays]

#Pack into pointer array
pointer_ar = (ctypes.POINTER(C.c_float) * count)(*ctypes_arrays)

ctypes.CDLL("./libfoo.so").foo(ctypes.c_int(count), pointer_ar, ctypes.c_int(size))

Where the C side of things might look like:

# function to multiply all arrays by 2
void foo(int count, float** array, int size)
{
   int ii,jj;
   for (ii=0;ii