Is it possible to return custom class from C++ dll?

Questions & Answers
1

I am writing a unmanaged plugin and I am trying to return a custom class from c++ to C#, I don’t think it’s possible but I am trying to check:

//Character.h
TESTFUNCDLL_API Character MakeCharacter(); 

class Character 
{
    int health;
    int magic;

public:
    ReturnCharacterClass()
    {
        return *this;
    }
}

//Character.cpp

Character MakeCharacter()
{
    Character cCharacter; 
	return cCharacter.ReturnCharacterClass();
}

//UseDll.cs

    [DllImport("Character", EntryPoint = "Character")]
    //How do I refrence character?! -public static extern int character();

Thanks in advance.

3

No, it’s not possible for several reasons:

  • First of all C# / .NET classes are located in managed heap memory.
  • C# / .NET classes have a different memory layout and class / type system.
  • C++ uses namemangeling for all exported symbols. Every C++ compiler uses it’s own mangeling rules.

What you usually can do is:

  • passing native object references to C# and interpret them as IntPtr. You can’t do anything on the C# side with it beside passing it back to a native code method where the C++ code can use the class pointer. Keep in mind that allocated memory on the native side has to be managed by yourself.
  • Native plugins can use extern "C" to export static methods without name mangeling which can be used by managed code.
  • C# code can allocate and “pin” managed memory and pass a reference to an exported C method and fill that memory with data. Scope and extent of that memory has to be taken care of.
2

You are going to want to exchange the data as though you are writing a server/client. I don’t know if C# can interpret binary data, but I would definitely give it a shot. You could have a struct with your native types, return that, and cast it back into a similar struct in C#. You may get mismatches for size of things though.

A safer route is to exchange using json or bson. Just return a json representation as a string and parse that in Unity.