COM介面必須得提供給客戶程式，這樣他們才能知道你的這個DLL存在什麼樣的函式實現什麼樣的功能，同時還需要一個GUID和介面ID。COM的介面你可以把它當成一個虛類處理。

定義介面如下：mycom.h

#pragma once #include "unknwn.h" // {85F5CF11-2A25-4ef9-8F7C-8C3F14A0860A} static const GUID CLSID_MyCOM = { 0x85f5cf11, 0x2a25, 0x4ef9, { 0x8f, 0x7c, 0x8c, 0x3f, 0x14, 0xa0, 0x86, 0xa } }; // {07C4A7BC-BBD1-4ced-80A5-A76377929F35} static const IID IID_ITest = { 0x7c4a7bc, 0xbbd1, 0x4ced, { 0x80, 0xa5, 0xa7, 0x63, 0x77, 0x92, 0x9f, 0x35 } }; interface ITest : public IUnknown { STDMETHOD (Add)(int nOp1, int nOp2, int* pret) PURE; };

介面實現如下：test.h

#pragma once #include "mycom.h" extern LONG g_cLock; // # of outstanding objects class CTest : public ITest { public: CTest(void); virtual ~CTest(void); public: // IUnknown members //@cmember Request an Interface STDMETHODIMP QueryInterface(REFIID, LPVOID *); //@cmember Increments the Reference count STDMETHODIMP_(ULONG) AddRef(void); //@cmember Decrements the Reference count STDMETHODIMP_(ULONG) Release(void); STDMETHOD (Add)(int nOp1, int nOp2, int* pret); protected: //@cmember Reference count ULONG m_cRef; };

test.cpp

#include "stdafx.h" #include "test.h" CTest::CTest(void) { m_cRef = 0; InterlockedIncrement(&g_cLock); } CTest::~CTest(void) { InterlockedDecrement(&g_cLock); } STDMETHODIMP CTest::QueryInterface(REFIID riid, void **ppv) { if(!ppv) return E_INVALIDARG; *ppv = NULL; if(riid == IID_IUnknown || riid == IID_ITest) *ppv = (LPVOID) this; if(*ppv == 0) return E_NOINTERFACE; ((LPUNKNOWN)*ppv)->AddRef(); return S_OK; } STDMETHODIMP_(ULONG) CTest::AddRef() { return ++m_cRef; } STDMETHODIMP_(ULONG) CTest::Release() { if(!--m_cRef) delete this; return m_cRef; } STDMETHODIMP CTest::Add(int nOp1, int nOp2,int * pret) { *pret = nOp1 + nOp2; return S_OK; }

將介面加入mycom中：factory.cpp

#include "test.h" STDMETHODIMP CClassFactory::CreateInstance(IUnknown* pUnkOuter, REFIID riid, void** ppv) { HRESULT hrRet; CTest* pTest = 0; if(NULL != pUnkOuter) return CLASS_E_NOAGGREGATION; if(IsBadWritePtr(ppv, sizeof(void*))) return E_POINTER; pTest = new CTest; if(NULL == pTest) return E_OUTOFMEMORY; hrRet = pTest->QueryInterface(riid, ppv); if(FAILED(hrRet)) delete pTest; return hrRet; }

至此一個簡單的COM程序內元件實現完成，其提供的介面是ITest，客戶程式可以通過這個介面呼叫CTest::Add函式。