helloworld.cpp

// Clearly the best hello world out there.
#define _ATL_ATTRIBUTES 1
#define _WINDLL 1
#include <atlbase.h>
#include <atlcom.h>
#include <string.h>
#include <comdef.h>
#include <string>
#include <fstream>
#include <iostream>

[module(name = "HelloWorld")];

[object, uuid("08FA02D2-21F4-11E8-B467-0ED5F89F718B"), library_block]
__interface IMessageFactory : IUnknown {
	// interesting it doesnt allow me to use std::string as a param
	[id(0)] void InternalPrintToConsole(BSTR *str);
};

[coclass, uuid("883F0C9E-21F5-11E8-B467-0ED5F89F718B")]
class MessageFactory : public IMessageFactory {

private:

	void InternalPrintToConsole(BSTR *str) {
		std::wstring wstr;
		wstr.assign(reinterpret_cast<WCHAR *>(*str));
		std::wcout << wstr << std::endl;
	}

public:
	MessageFactory() {
	}

	~MessageFactory() {
	}

	void PrintStringToConsole(_bstr_t str) {
		this->InternalPrintToConsole(&str.GetBSTR());
	}
};

MessageFactory *CreateMessageFactory() {
	CComObject<MessageFactory> *msg_fac;
	if (SUCCEEDED(CComObject<MessageFactory>::CreateInstance(&msg_fac))) {
		return msg_fac;
	}

	std::ifstream fail_msg("Unable to create message factory!");
	fail_msg.exceptions(fail_msg.failbit);
}

int main(int argc, char **argv) {
	try {
		if (SUCCEEDED(CoInitialize(NULL))) {
			MessageFactory *message_factory = CreateMessageFactory();
			_bstr_t hello_str("Hello World!");
			message_factory->PrintStringToConsole(hello_str);
		} else {
			std::ifstream fail_msg("CoInitalize failed!");
			fail_msg.exceptions(fail_msg.failbit);
		}
	}
	catch (std::exception &ex) {
		std::cout << ex.what() << std::endl;
	}
	return 0;
}

Note that usage of ATL attributes is deprecated and produces warning C4467.

I was doing this in C#.