how to return a numpy array to python from c++ (shared memory)

edit

That's bull**. Anyone can learn to code C++, because it's natural.

Unfortunately, my users do not have interest or time to learn c++. I wish you are my target user :-). Anyway, thanks for your comment.

Is this not where you need a function like DLLEXPORT char *alloc_img(const char *file_name, int *width, int *height, size_t *image_id)?

.. and also a function like... DLLEXPORT int free_img(size_t *image_id)

... and also the Python code:

width = ct.pointer(ct.c_int())
height = ct.pointer(ct.c_int())
img_id = ct.pointer(ct.c_size_t())
s = "dove.png"
lib = ct.CDLL("void_dll.dll")
alloc_img = lib.alloc_img
free_img = lib.free_img
alloc_img.restype = ct.c_char_p

bytes_array = alloc_img(ct.c_char_p(s.encode("utf-8")), width, height, img_id)
numpy_array = np.frombuffer(bytes_array, dtype=np.uint8)
...    
free_img(img_id)

I think you must have misunderstood my question.

Instead of letting user retrieve the shared memory pointer, create a numpy array and shape it to the correct dimemsion, I would like to let the user achieve that by a single function call from C++ app to retrieve the numpy array (i.e. without performing the following code line 2 to 3):

Original solution:

import myLib;
imgPtr = myLib.GetImgBuffer(img1, cols1, rows1) 
numpy_array = np.frombuffer(imgPtr, dtype=np.uint8)
numpy_array.shape = (rows1, cols1)

instead:

New Solution:

import myLib
retreiveNPArray = myLib.GetNumpyArray();

--> this retrieves the numpy array created in c++ with the correct shape (and is using shared memory with Python, so any python related updated on this array will be reflected in c++ automatically)

The original solution requires user to understand the programming basics of retrieving the buffer pointer, create a numpy array from buffer pointer and then shape the numpy array accordingly. For my users, they will ask me "Why do I have to do all that? This is too complicated. Why can't you just give me the numpy array in Python for the displayed image on C++ app?"

So, you've figured it out? That's good!

Sorry, yes I do believe that I have misunderstood you.

no, I am still looking for a solution...I am still researching how to implement GetNumpyArray() on the c++ side...

I think I can use PyArray_SimpleNewFromData()... but I got access violation error with the following code:

assuming it is a 512x512 int8 image and buf is the:

 void pointer* (image data)
            PyObject* Py_Image::GetNumArray()
            {
....

                npy_intp m[1] = { 512 };
                PyObject* pNdArray = PyArray_SimpleNewFromData(512, m, NPY_INT, buf); <----access violation error
                return pNdArray;
            }

Am I not calling PyArray_SimpleNewFromData() properly?