Named shared memory between C++ and python on Windows

I'm working on a C++ application that exchanges data with a Python script through named shared memory on Windows. I'm facing a problem where the Python script displays a completely black image as if it's reading all zeros from the memory. I suspect there might be an issue with the code.

In the C++ application, I'm using Boost.Interprocess library for shared memory operations. Here's the code:

#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/mapped_region.hpp>
#include <iostream>
#include <fstream>

using namespace boost::interprocess;
#define SHM_NAME "SharedMemory"
#define BYTES_NUMBER 541798 // Image size is 529 KB

int main()
{
    shared_memory_object shm(open_or_create, SHM_NAME, read_write);
    shm.truncate(BYTES_NUMBER);

    mapped_region region(shm, read_write);

    std::ifstream imageFile("input.bmp", std::ios::binary);
    if (!imageFile)
    {
        std::cerr << "Failed to open the image file." << std::endl;
        return 1;
    }

    std::copy(std::istreambuf_iterator<char>(imageFile), std::istreambuf_iterator<char>(), static_cast<char*>(region.get_address()));
    imageFile.close();
    std::cout << "Image successfully written to shared memory." << std::endl;

    // Launch Python script
    std::string command = "python sharedMemory.py";
    std::system(command.c_str());

    std::cout << "Press any key to exit." << std::endl;
    _getch();

    return 0;
}

In the Python script, I'm using the mmap module to read the image data from shared memory. Here's the script:

import mmap
from PIL import Image

SHM_NAME = "SharedMemory"
BYTES_NUMBER = 541798
IMAGE_WIDTH = 511
IMAGE_HEIGHT = 265

if __name__ == "__main__":
    shm = mmap.mmap(-1, BYTES_NUMBER, SHM_NAME)
    image_data = shm.read(BYTES_NUMBER)
    shm.close()

    image = Image.frombytes("RGB", (IMAGE_WIDTH, IMAGE_HEIGHT), image_data, "raw")
    image.show()

When running the code, the image displayed by the Python script appears completely black. I suspect that the issue might be related to how I'm writing/reading the image data on the shared memory.

This first thing I notice in your python script is line 10. When I run your code, my IDE tells me that the third argument is invalid because it is a string
shm = mmap.mmap(-1, BYTES_NUMBER, SHM_NAME). I would change it to something like shm = mmap.mmap(-1, BYTES_NUMBER, access=mmap.ACCESS_READ, offset=0). The access parameter has three options: ACCESS_READ, ACCESS_WRITE, ACCESS_COPY. Try playing around with that parameter and see if that changes anything. The offset argument is often specified as 0 when we want to map the file from the start address. References: <https://www.askpython.com/python-modules/mmap-function>, <https://docs.python.org/3/library/mmap.html>