C++ plugin for Unity “EntryPointNotFoundExeption”

I need some serious help here... I'm trying to either get my member functions exported so I can call them in C#

WMIWrapper.h

 #ifndef _WMIWRAPPER_H_
 #define _WMIWRAPPER_H_
 
 #include <Windows.h>  
 #include <sstream>  
 #include <iostream>
 #include <WbemCli.h>  
 
 using std::endl;
 using std::wstring;
 using std::wstringstream;
 
 #pragma comment(lib, "wbemuuid.lib")  
 
 static class WMIWrapper 
 {  
 public:
  __declspec(dllexport) WMIWrapper();
  __declspec(dllexport) ~WMIWrapper();
 
  __declspec(dllexport) wstring CreateCOM();
  __declspec(dllexport) wstring CreateService();
 __declspec(dllexport) wstring GetMonitors();
 
 private:
  IWbemLocator* _locator;
  IWbemServices* _service;
  IEnumWbemClassObject* _monitors;
 };
 
 #endif

WMIWrapper.cpp

 #include "WMIWrapper.h"
 
 
 extern "C" {
 
  WMIWrapper::WMIWrapper()
  {
  _locator = NULL;
  _service = NULL;
  }
 
  WMIWrapper::~WMIWrapper()
  {
  if(_service != NULL)
  _service->Release();
  if(_locator != NULL)
  _locator->Release();
  }
 
  wstring WMIWrapper::CreateCOM()
  {
  wstringstream ERRStream (wstringstream::in | wstringstream::out);
  HRESULT hRes = CoInitializeEx(NULL, COINIT_MULTITHREADED);  
  if(FAILED(hRes))  
  {  
  ERRStream << "Unable to launch COM: 0x" << std::hex << hRes << endl;
  return L"";  
  }  
 
  hRes = CoInitializeSecurity(NULL, -1, NULL, NULL, RPC_C_AUTHN_LEVEL_CONNECT, RPC_C_IMP_LEVEL_IMPERSONATE, NULL, EOAC_NONE, 0);
  if(FAILED(hRes))
  {
  ERRStream << "Unable to set security level for COM: " << std::hex << hRes << endl;
  return L"";
  }
 
  if(FAILED(hRes = CoCreateInstance(CLSID_WbemLocator, NULL, CLSCTX_ALL, IID_PPV_ARGS(&_locator))))  
  {  
  ERRStream << "Unable to create a WbemLocator: " << std::hex << hRes << endl;  
  return L"";  
  }
 
  const std::wstring& myWString = ERRStream.str();
  const LPCWSTR p = myWString.c_str();
  return p;
 
  }
 
  wstring WMIWrapper::CreateService()
  {
  wstringstream ERRStream (wstringstream::in | wstringstream::out);
  HRESULT hRes;
  if(_locator == NULL || FAILED(hRes = _locator->ConnectServer(L"root\\CIMV2", NULL, NULL, NULL, WBEM_FLAG_CONNECT_USE_MAX_WAIT, NULL, NULL, &_service)))  
  {  
  ERRStream << "Unable to connect to \"CIMV2\": " << std::hex << hRes << endl;  
  return L"";  
  }  
 
  const std::wstring& myWString = ERRStream.str();
  const LPCWSTR p = myWString.c_str();
  return p;
  }
 
  wstring WMIWrapper::GetMonitors()
  {
  HRESULT hRes;
  wstringstream ssMonitorDescription;
  if(_locator == NULL 
  || _service == NULL
  || FAILED(hRes = _service->ExecQuery(L"WQL", L"SELECT * FROM Win32_DesktopMonitor", WBEM_FLAG_FORWARD_ONLY, NULL, &_monitors)))
  {
  //ERRStream << "Unable to retrieve desktop monitors: " << std::hex << hRes << endl;
  return L"";
  }
 
  IWbemClassObject* clsObj = NULL;
  int numElems;
  while((hRes = _monitors->Next(WBEM_INFINITE, 1, &clsObj, (ULONG*)&numElems)) != WBEM_S_FALSE)
  {
  if(FAILED(hRes))
  break;
 
  VARIANT vRet;
  VariantInit(&vRet);
  if(SUCCEEDED(clsObj->Get(L"Description", 0, &vRet, NULL, NULL)) && vRet.vt == VT_BSTR)
  {
  //std::wcout <<  L"Description: " << vRet.bstrVal << endl;
  ssMonitorDescription << "Description: " << vRet.bstrVal << endl;
  VariantClear(&vRet);
  }
  }
 
  clsObj->Release();
 
  return ssMonitorDescription.str();
  }
 }

Unity Script

 using UnityEngine;
 using System.Runtime.InteropServices;
 using System;
 
 
 public class HardwareDiagnostics : MonoBehaviour {
  
  [DllImport("WMIWrapper", EntryPoint="CreateCOM", CharSet = CharSet.Unicode)]
  static extern String CreateCOM();
  
  [DllImport("WMIWrapper", EntryPoint="CreateService", CharSet = CharSet.Unicode)]
  static extern String CreateService();
  
  [DllImport("WMIWrapper", EntryPoint="GetMonitors", CharSet = CharSet.Unicode)]
  static extern String GetMonitors();

  
  // Use this for initialization
  void Start () {
 
  CreateCOM();
  CreateService();
  Debug.Log(GetMonitors());
     
  }
  
  // Update is called once per frame
  void Update () {
  
  }
  
   
 }

So I'm trying to call those member functions from the Unity script and I'm getting the EntryPointNotFoundExeption error. I thought maybe it was because you couldn't export member functions, so I tried writing that "Interface.cpp" to execute those functions and return the result but that returns the same error.

UPDATE

Per suggestion I have changed my C++ functions to this format

 void WMIWrapper::CreateCOM(wchar_t* err, int errLength)
  {
  .../Determine wstringstream ERRStream

 
  wcscpy_s(err, errLength, ERRStream.str().c_str());
 
  }

And my C# like so:

 public class HardwareDiagnostics : MonoBehaviour {
  
  [DllImport( "WMIWrapper", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
  private static extern void CreateCOM(StringBuilder str, int length);
  
  [DllImport( "WMIWrapper", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
  private static extern void CreateService(StringBuilder str, int length);
  
  [DllImport( "WMIWrapper", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
  private static extern void GetMonitors(StringBuilder str, int length);
  
  // Use this for initialization
  void Start () {
  StringBuilder buffer = new StringBuilder(255);
  
  CreateCOM(buffer, buffer.Capacity);
  Debug.Log(buffer.ToString());
  
  CreateService(buffer, buffer.Capacity);
  Debug.Log(buffer.ToString());
  
  GetMonitors(buffer, buffer.Capacity);
  Debug.Log(buffer.ToString());
  
  }
  
  // Update is called once per frame
  void Update () {
  
  }
  
   
 }

HOWEVER, I'm still getting "EntryPointNotFoundExeption" when calling the first function, CreateCOM();