Python Bindings with C-CodePudding

I am interested in writing functions in C that can later be "imported" in Python. For example I wrote a simple function in C that adds two int numbers:

//function declaration
int addition(int a,int b);

//function definition
int addition(int a,int b)
{
    return (a b);
}

I also have a header file which contains:

extern "C" MATHLIBRARY_API int addition(int a, int b);

Then in Python the code is straightforward due to the help of ctypes:

import ctypes

path = "C:\\my path to the .dll file"

# load the library
lib = ctypes.CDLL('{0}\MathLibrary.dll'.format(path))
answer = lib.addition(14, 2)
print(answer) // OUTPUT: 16

Everything works good so far, but I would like to do some math with more complex data structures such as vectors. I would like to have a vector of elements (example: {12, 10, 2, 14}) and add a number to all of the elements inside the vector. For example, n = 2, vector = {12, 10, 2, 14}, output = {14, 12, 4, 16}. I wrote a function that works in C but I can't manage to do the binding to Python. I believe that is due to the fact I am working with vectors and that extern "C" in the header file.

CodePudding user response：

ctypes only allows you to interact with a library using C types, not C . boost.python, pybind11, etc allow you pass C objects.

However, there is a way to do what you want to do in ctypes using C-style arrays.

Declare a function like this:

extern "C" MATHLIBRARY_API void addToArray(int *array, int num, int size);

and define it like this:

void addToArray(int *array, int num, int size)
{
    for (int i=0; i < size;   i)
    {
        array[i] = array[i]   num;
    }
}

Then in your Python script do this:

nums = [12, 10, 2, 14]
array_type = ctypes.c_int * len(nums)
lib.additionArray.argtypes = [ctypes.POINTER(ctypes.c_int), ctypes.c_int, ctypes.c_int]
array = array_type(*nums)
lib.addToArray(array, ctypes.c_int(2), ctypes.c_int(len(nums)))
# copy modified array into original list
nums[:] = list(array)
print(nums)