一个COM演示代码

#include "stdafx.h"

#include <iostream>
using namespace std;
#include <objbase.h>

void trace(const char* msg) 
{ 
	cout << msg << endl;
}

// interface definition
interface IX : IUnknown
{
	virtual void __stdcall Fx() = 0;
};

interface IY : IUnknown
{
	virtual void __stdcall Fy() = 0;
};

interface IZ : IUnknown
{
	virtual void __stdcall Fz() = 0;
};

// Forward references for GUIDs
extern const IID IID_IX;
extern const IID IID_IY;
extern const IID IID_IZ;

//
// implement interface IX,IY (A COM component）
//
class CA : public IX, public IY
{
	// IUnknown implementation
	virtual HRESULT __stdcall QueryInterface(const IID& iid, void** ppv);            
	virtual ULONG __stdcall AddRef() { return 0;}
	virtual ULONG __stdcall Release() { return 0;}

	// Interface IX implementation
	virtual void __stdcall Fx() { cout << "This is Fx func" << endl;}

	// Interface IY implementation
	virtual void __stdcall Fy() { cout << "This is Fy func" << endl;}
};

HRESULT __stdcall CA::QueryInterface(const IID& iid, void** ppv)
{     
	if (iid == IID_IUnknown)
	{
		trace("QueryInterface: Return pointer to IUnknown.");
		*ppv = static_cast<IX*>(this);
	}
	else if (iid == IID_IX)
	{
		trace("QueryInterface: Return pointer to IX.");
		*ppv = static_cast<IX*>(this);
	}
	else if (iid == IID_IY)
	{
		trace("QueryInterface: Return pointer to IY.");
		*ppv = static_cast<IY*>(this);
	}
	else
	{         
		trace("QueryInterface: Interface not supported.");
		*ppv = NULL;
		return E_NOINTERFACE;
	}
	reinterpret_cast<IUnknown*>(*ppv)->AddRef(); // add reference num

	return S_OK;
}

//
// create class CA, return a pointer to IUnknown
//
IUnknown* CreateInstance()
{
	IUnknown* pI = static_cast<IX*>(new CA);
	pI->AddRef();
	return pI ;
}

//
// IID of interfaces
//
// {32bb8320-b41b-11cf-a6bb-0080c7b2d682}
static const IID IID_IX = 
{0x32bb8320, 0xb41b, 0x11cf,
{0xa6, 0xbb, 0x0, 0x80, 0xc7, 0xb2, 0xd6, 0x82}};

// {32bb8321-b41b-11cf-a6bb-0080c7b2d682}
static const IID IID_IY = 
{0x32bb8321, 0xb41b, 0x11cf,
{0xa6, 0xbb, 0x0, 0x80, 0xc7, 0xb2, 0xd6, 0x82}};

// {32bb8322-b41b-11cf-a6bb-0080c7b2d682}
static const IID IID_IZ = 
{0x32bb8322, 0xb41b, 0x11cf,
{0xa6, 0xbb, 0x0, 0x80, 0xc7, 0xb2, 0xd6, 0x82}};

//
// main functionclient)
//
int _tmain(int argc, _TCHAR* argv[])
{
	HRESULT hr;

	trace("Client:get IUnknown pointer.");
	IUnknown* pIUnknown = CreateInstance();

	trace("Client:get interface IX.");
	IX* pIX = NULL; 
	hr = pIUnknown->QueryInterface(IID_IX, (void**)&pIX);
	if (SUCCEEDED(hr))
	{
		trace("Client: Succeeded getting IX.");
		pIX->Fx();          // using IX.
	}

	trace("Client:get interface IY.");
	IY* pIY = NULL;
	hr = pIUnknown->QueryInterface(IID_IY, (void**)&pIY);
	if (SUCCEEDED(hr))
	{
		trace("Client: Succeeded getting IY.");
		pIY->Fy();          // using IY.
	}

	trace("Client:whether support interface IZ.");
	IZ* pIZ = NULL;
	hr = pIUnknown->QueryInterface(IID_IZ, (void**)&pIZ);
	if (SUCCEEDED(hr))
	{
		trace("Client: Succeeded getting IZ.");
		pIZ->Fz();
	}
	else
	{
		trace("Client: Failed getting IZ，can't support IZ.");
	}

	trace("Client:using interface IX to query interface IY.");
	IY* pIYfromIX = NULL;
	hr = pIX->QueryInterface(IID_IY, (void**)&pIYfromIX);
	if (SUCCEEDED(hr))
	{    
		trace("Client: Succeeded getting IY.");
		pIYfromIX->Fy();
	}

	trace("Client:using interface IY query interface IUnknown.");
	IUnknown* pIUnknownFromIY = NULL;
	hr = pIY->QueryInterface(IID_IUnknown, (void**)&pIUnknownFromIY);
	if (SUCCEEDED(hr))
	{
		cout << "pIUnknownFromIY equal to IUnknown ?";
		if (pIUnknownFromIY == pIUnknown)
		{
			cout << "Yes, pIUnknownFromIY == pIUnknown." << endl;
		}
		else
		{
			cout << "No, pIUnknownFromIY != pIUnknown." << endl;
		}
	}

	// Delete the component.
	delete pIUnknown;

	return 0;
}