《COM技术内幕》代码之 接口的实现，QueryInterface的实现，QueryInterface的使用

#include <iostream> #include <atlbase.h> using namespace std; interface IX : public IUnknown { virtual void _stdcall Fx() = 0; }; interface IY : public IUnknown { virtual void _stdcall Fy() = 0; }; interface IZ : public IUnknown { virtual void _stdcall Fz() = 0; }; static const IID IID_IX = {0xff5ba880, 0xa371, 0x4a42, {0x87, 0x20, 0x96, 0xe0, 0x4d, 0x68, 0xd, 0x76}}; // {FF5BA880-A371-4a42-8720-96E04D680D76} static const IID IID_IY = {0xde44d538, 0xe926, 0x4d5f, {0x94, 0x5d, 0x61, 0x83, 0x86, 0x7c, 0x63, 0x41}}; // {DE44D538-E926-4d5f-945D-6183867C6341} static const IID IID_IZ = {0x91157d15, 0x22b1, 0x45d9, {0xb4, 0xc9, 0x81, 0x3, 0x8d, 0xec, 0xef, 0xad}}; // {91157D15-22B1-45d9-B4C9-81038DECEFAD} class CA : public IX, public IY { public: virtual HRESULT _stdcall QueryInterface(REFIID riid, __RPC__deref_out void **ppvObject); virtual ULONG _stdcall AddRef() { return 0; } virtual ULONG _stdcall Release() { return 0; } virtual void _stdcall Fx() { cout<<"IX::Fx"<<endl; } virtual void _stdcall Fy() { cout<<"IY::Fy"<<endl; } }; HRESULT _stdcall CA::QueryInterface(REFIID riid, __RPC__deref_out void **ppvObject) { if(IID_IX == riid) { *ppvObject = static_cast<IX*>(this); } else if(IID_IY == riid) { *ppvObject = static_cast<IY*>(this); } else if(IID_IUnknown == riid) { //*ppvObject = static_cast<IUnknown*>(this); //这样为什么不行 *ppvObject = static_cast<IX*>(this); } else { *ppvObject = NULL; return E_NOINTERFACE; } reinterpret_cast<IUnknown*>(*ppvObject)->AddRef(); return S_OK; } IUnknown* CreateInstance() { IUnknown *pIUnk = static_cast<IX*>(new CA); pIUnk->AddRef(); return pIUnk; } void _tmain(int argc,_TCHAR*argv[]) { IUnknown *pIUnk = CreateInstance(); IX *pIX = NULL; HRESULT hr = pIUnk->QueryInterface(IID_IX,(void**)&pIX); if(SUCCEEDED(hr)) { pIX->Fx(); } IY *pIY = NULL; hr = pIUnk->QueryInterface(IID_IY,(void**)&pIY); if(SUCCEEDED(hr)) { pIY->Fy(); } IZ *pIZ = NULL; hr = pIUnk->QueryInterface(IID_IZ,(void**)&pIZ); if(SUCCEEDED(hr)) { cout<<"Succeed to find pIZ"<<endl; pIZ->Fz(); } IY *pIYFromIX = NULL; hr = pIX->QueryInterface(IID_IY,(void**)&pIYFromIX); if(SUCCEEDED(hr)) { pIYFromIX->Fy(); } IUnknown *pIUnkFromIY = NULL; hr = pIY->QueryInterface(IID_IUnknown,(void**)&pIUnkFromIY); if(SUCCEEDED(hr)) { if(pIUnkFromIY == pIUnk) cout<<"pIUnkFromIY == pIUnk"<<endl; else cout<<"pIUnkFromIY != pIUnk"<<endl; } if(pIUnk) delete pIUnk; }