How transferring an image to buffer in c++(dll) and then read/write in buffer in C#?

Question

How transferring an image to buffer in c++(dll) and then read/write in buffer in C# and return to c++(dll) in real time? The process I'm looking is in the following :

1- First, I read an image form hard drive; Mat inputImage = read(“/,…./Test.jpg”);

2- Put in the buffer:

imencode(".jpg", inputImage, inputBuff, paramBuffer);

3- send form c++ to c# ??? (I don't know).

4- read in c# from buffer ??? (I don't know).

5- write the changes that happens through c++ and c# in buffer ??? (I don't know).

I'm using Opencv c++.

I really thank you.

Answer 1

You can use System.Runtime.InteropServices in C# to call functions in external libraries, for example

c++ code

extern "c"
{
    __declspec(dllexport) void __cdecl Read(unsigned char*& buffer)
    {
        //allocate and write to buffer
    }

    __declspec(dllexport) void __cdecl Write(unsigned char* buffer)
    {
        //do something with the buffer
    }
}

and compile it into a dll

C# code

using System.Runtime.InteropServices;

class Main
{
    [DllImport(DLL_FILE, CallingConvention = CallingConvention.Cdecl)]
    private static extern void Read(out IntPtr buffer);

    [DllImport(DLL_FILE, CallingConvention = CallingConvention.Cdecl)]
    private static extern void Write(byte[] buffer);

    public static void ReadFromExtern()
    {
        IntPtr bufferPtr = IntPtr.Zero;
        Read(bufferPtr);

        int length = LENGTH;
        byte[] buffer = new byte[length];        
        Marshal.Copy(bufferPtr, buffer, 0, length);
        //do something with buffer
    }

    public static void WriteToExtern(byte[] buffer)
    {
        Write(buffer);
        //or do something else
    }
}

Note:

1. If you used dynamically allocated memory in the c++ code, remember to also write a wrapper function to free it, otherwise causing memory leak.

2. __declspec(dllexport) is Windows specific to export functions to dll(s).

3. extern "C" is to avoid name mangling by c++ compilers, can be omitted if using c compilers

4. For string transferring, use char* in c++ and System.Text.StringBuilder in c#