Pass structure (or class) from C++ dll to C# (Unity 3D)

Question

I am writing a wrapper to get some data from a sensor. While I have no problems with passing int, float and arrays of them, I have difficulties to grasp how to pass a structure.

Code summary

C++ side

The structure is as follows:

struct HandInfo
{
    int id;
    float x, y, z;
};

At some point one static, globally visible HandInfo leftHand is filled with values which are retrievable through the following wrapper function:

extern EXPORT_API HandInfo MyWrapper_getLeftHand()
{
    return handtracker.getLeftHand();
}

where handtracker is just an instance of the wrapped class.

C# side

Once declared the extern function

[DllImport("MyWrapper")]
private static extern HandInfo MyWrapper_getLeftHand();

On the C# side, ideally, I would have the same struct type

public struct HandInfo
{
    public int id;
    public float x, y, z;
}

and assign a variable

HandInfo hi = MyWrapper_getLeftHand(); // NAIVELY WRONG CODE

which, understandably, doesn't work.

What's the way to achieve this?

I'd appreciate any help. Thank you all for your time.

Answer 1

It should work correctly (at least, here in a small C++ + C# project I have, I was able to make it work with that struct, both in x86 and x64)

[DllImport("MyWrapper.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern HandInfo MyWrapper_getLeftHand();

The only thing, you must declare the CallingConvention = CallingConvention.Cdecl.