Basics for a plugin with C++ DLL

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Hello everyone,

I am currently starting the process of coding a small plugin for Overwolf that will let me display onscreen information that I gather from a DLL that I write in C++ (e.g. some information on the system's state, CPU, memory, etc... network status and more).

I had a look at the up to date plugin sample (https://github.com/overwolf/overwolf-plugin-sample), unfortunately this is in C# and I do not practice nor clearly understand this programming language (yet!).

To get started I would like to simply modify the sample plugin so when it loads it retrieves an integer from my DLL, I think if I have that working I can manage the rest.

I tried to recreate the C# DLL in C++ but it fails miserably, the plugin simply does not even load.
First I had to create a main.cpp with the DllMain entry point, otherwise my compiler was screaming to death (perhaps that might be a problem), then I recreated the general structure of the DLL but it still does not work.
Here is what I attempted:

namespace overwolf {
	namespace samples {
		namespace plugins {
			class SamplePlugin {
				int SampleProperty = 55;
				//int SampleProperty(); // Also tried to return it from a member function, didn't work

I tried without the namespaces too, no more luck.
In the JavaScript files that are supposed to load the plugin (main.js) the first lines are:

// create an instance of the plugin
var plugin = new OverwolfPlugin("OverwolfSamplePlugin", true);

// initialize it
plugin.initialize(function(status) {
  // ...

Nothing past plugin.initialize gets executed so I deduce that the plugin just fails to load (the dll is in the right directory with the right name, if I place the compiled C# DLL then it does work).

Is there the equivalent of the C# sample plugin DLL in C++ somewhere?
Otherwise could anyone guide me on how to make my C++ DLL work and being able to call its functions from the HTML/JavaScript please?

I am sure that for someone used to the Overwolf's plugin system this will be easy, as there are several things that I don't quite get (I have only done standalone executable and DLL loaded "classically" from their entry point, never done a plugin before.

Thank you very much for your help.

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You need to export methods from your c++ library, so that they are accessible from outside world.
Create an DLL export definition file:

LIBRARY "YourNameHere"

    Start	@1
    Stop	@2
    OnError	@3

Then you need a c# plugin, just use the one from example and add this:

        [DllImport("YourNameHere.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern void Start();

        [DllImport("YourNameHere.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern void Stop();

        [DllImport("YourNameHere.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern void OnError(IntPtr pfCallback);

       // Only needed for c++ callbacks
       public delegate void Register([MarshalAs(UnmanagedType.LPWStr)] string Base64Stream);
       Register FuncPtrCallbackOnError;

      // Called every time you start the c# plugin to register callbacks
      FuncPtrCallbackOnError = new Register(yourfuinctionhere); // Define that function it is the one that will be called from c++
     // No callbacks needed, then just call the function you need

Like you can see OnError has a parameter, it is a callback function, you need to define this in your c++ library and use in callback function, for example like this:

typedef void(__stdcall * _ManagedCallbackOnError)(wchar_t Data[]);
static _ManagedCallbackOnError ManagedCallbackOnError;

// This is the exported method (available to call from c# plugin)
void OnError(_ManagedCallbackOnError ManagedCallback)
	ManagedCallbackOnError = ManagedCallback;

void Stop()

void Start()


// Call c# callback function
std::wstring Err(L"0x0001");
ManagedCallbackOnError((wchar_t *)Err.c_str());

Besides that, everything is same as in c# plugin so just define your callback function "yourfuinctionhere" and use info received from the callback - for example by sending it back to javascript.

Hope that helps.

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