近期须要用到COM组件的知识，看了看COM编程指南，感觉还不错。把我的学习心得记录下来。这是我依据教程写的demo

StopWatch接口实现部分，接口部分我的项目是动态库，主要源代码例如以下：

完整demo见：http://download.csdn.net/detail/davidsu33/7750101

stopwatch.h

#pragma once

#include <Windows.h>

#include <MMSystem.h>

#include <Unknwn.h>

#include <WinBase.h>

#include "timer_i.h"

class stopwatcher

{

public:

	stopwatcher(void);

	~stopwatcher(void);

};

class IStopWatch : public IUnknown

{

public:

	//virtual unsigned long _stdcall Release() = 0;

	virtual HRESULT _stdcall Start() = 0;

	virtual HRESULT _stdcall ElaspedTime(float *elaspedtime) = 0;

};

class CStopWatch : public IStopWatch

{

public:

	CStopWatch()

	{

		m_nRefValue = 0;

		m_nFreq.QuadPart = 0;

		QueryPerformanceFrequency(&m_nFreq);

		AddRef();

	}

public:

	//virtual unsigned long _stdcall Release()

	//{

	//	delete this;

	//	return 0;

	//};

	//创建相应的接口对象

	virtual HRESULT STDMETHODCALLTYPE QueryInterface(

        /* [in] */ REFIID riid,

        /* [iid_is][out] */ __RPC__deref_out void __RPC_FAR *__RPC_FAR *ppvObject)

	{

		if(riid == IID_IStopWatch)

		{

			*ppvObject = static_cast<IStopWatch*>(this);

			return S_OK;

		}

		else if(riid == IID_IUnknown)

		{

			*ppvObject = static_cast<IUnknown*>(this);

			return S_OK;

		}

		*ppvObject = NULL;

		return E_NOINTERFACE;

	};

	//添加引用

    virtual ULONG STDMETHODCALLTYPE AddRef( void)

	{

		InterlockedIncrement(&m_nRefValue);

		return m_nRefValue;

	};

	//解除引用

    virtual ULONG STDMETHODCALLTYPE Release( void)

	{

		InterlockedDecrement(&m_nRefValue);

		if(m_nRefValue == 0)

			delete this;

		return m_nRefValue;

	};

	virtual HRESULT _stdcall Start()

	{

		BOOL bOK = QueryPerformanceCounter(&m_nStartTime);

		if(!bOK)

			return S_FALSE;

		return S_OK;

	};

	virtual HRESULT _stdcall ElaspedTime(float *elaspedtime)

	{

		LARGE_INTEGER nStopTime;

		BOOL bOK = QueryPerformanceCounter(&nStopTime);

		if(!bOK)

			return S_FALSE;

		*elaspedtime = ((float)(nStopTime.QuadPart - m_nStartTime.QuadPart))/m_nFreq.QuadPart;

		return S_OK;

	};

private:

	LARGE_INTEGER m_nFreq;

	LARGE_INTEGER m_nStartTime;

	volatile unsigned long m_nRefValue;

};

//return IStopWatch interface object

extern "C" HRESULT _stdcall DllGetClassObject(REFCLSID rcsid, REFIID rid, LPVOID* lpvoid)

{

	if(rcsid == CLSID_CStopWatch)

	{

		*lpvoid = static_cast<IStopWatch*>(new CStopWatch);

		return S_OK;

	}

	*lpvoid = NULL;

	return CLASS_E_CLASSNOTAVAILABLE;

}

client的调用代码

#include "../stopwatch/stopwatcher.h"

#include "../stopwatch/timer_i.h"

#include <iostream>

#include <cstring>

#include <cassert>

#define TIMERDLL L"../Debug/stopwatch.dll"

#define PROCNAME "DllGetClassObject"

typedef HRESULT  (_stdcall*  GETOBJFUNC)(REFCLSID , REFIID , LPVOID* );

using namespace std;

void trace(const char *str)

{

	cout<<str<<endl;

}

void trace(const string& s)

{

	cout<<s.c_str()<<endl;

}

HRESULT CreateInstance(void **p, HMODULE *rhMod)

{

	HMODULE hMod = LoadLibrary(TIMERDLL);

	if(!hMod)

		return E_FAIL;

	GETOBJFUNC proc =

		(GETOBJFUNC)GetProcAddress(hMod, PROCNAME);

	if(!proc)

		return E_FAIL;

	*p = proc;

	*rhMod = hMod;

	return S_OK;

}

void FreeInstance(HMODULE hMod)

{

	assert(FreeLibrary(hMod));

}

void testInstance()

{

	void *fptr = NULL;

	HMODULE hMod = NULL;

	HRESULT hr = CreateInstance(&fptr, &hMod);

	if(FAILED(hr))

	{

		trace("CreateInstace failed");

		return;

	}

	GETOBJFUNC proc = (GETOBJFUNC)(fptr);

	IUnknown *ptr = NULL;

	//首先得到类实例

	//然后依据类实例得到IUnknown

	//最后通过IUnknown调取QueryInterface接口来得到其子类的接口对象

	//调用子类的接口对象

	hr = proc(CLSID_CStopWatch, IID_IUnknown, (LPVOID*)&ptr);

	if(FAILED(hr))

	{

		trace("GetObject failed");

		return;

	}

	if(!ptr)

	{

		trace("ptr is null");

		return;

	}

	IStopWatch *ptrSW = NULL;

	hr = ptr->QueryInterface(IID_IStopWatch, (void**)&ptrSW);

	assert(SUCCEEDED(hr));

	hr = ptrSW->Start();

	assert(SUCCEEDED(hr));

	int m=0;

	for(int i=0; i<10000000; ++i)

		++m;

	float elaspedtime = 0;

	hr = ptrSW->ElaspedTime(&elaspedtime);

	assert(SUCCEEDED(hr));

	cout<<"ElaspedTime:"<<elaspedtime<<endl;

	//释放对象本身

	ptrSW->Release();

	FreeInstance(hMod);

}

int main(int argc, char *argv[])

{

	testInstance();

	getchar();

	return 0;

}