Returning string data from c++ dll does not work

TDL:

[Field: Test Fld]
Use : Name Field
Set as : "Hello"+ @SomeString
Set Always : Yes
Read Only : Yes
SomeString:$$CallDllFunction: Project3:HelloWorld3

--------------------

C++

#include <windows.h>
#include <iostream>
#include <string>
using namespace std;
#include <OleAuto.h>

//does not work
extern "C" __declspec(dllexport) wchar_t* __stdcall HelloWorld3()
{
wchar_t* c = (wchar_t*) "Hello World";
return SysAllocString(c);
}

//does not work
extern "C" __declspec(dllexport) const char* __stdcall HelloWorld4() {
return "Hello World";
}

What data type syntax to use so that the returned string is displayed in TDL field ??

Thanks in advance..

 

has anyone got workaround for sending and retrieving string data from a standard C++ dll ?