QueryInterface函数

// //IUnkown.cpp // // #include <iostream.h> #include <objbase.h> void trace(const char * msg) {cout << msg << endl ;} //Interface 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; // //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 << “Fx” << endl ;} //Interface IY implementation virtual void __stdcall Fy() {cout << “Fy” << 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(); return S_OK; } // //Creation function // IUnknown* CreateInstance() { IUnknown* pI = static_cast< IX* >(new CA); pI->AddRef(); return pI; } // //IIDs // //{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}}; // //Client // int main() { HRESULT hr; trace(“Client:Get an 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(); //Use interface 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(); //Use interface IY } trace(“Client:Get 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:Could not get interface IZ.”); } trace(“Client:Get interface IY from interface IX.”); IY* pIYfromIX = NULL; hr = pIX->QueryInterface(IID_IY, (void**)&pIYfromIX); if(SUCCEEDED(hr)) { trace(“Client:Succeeded getting IY.”); pIYfromIX->Fy(); } trace(“Client:Get interface IUnknown from IY.”); IUnknown* pIUknownFromIY = NULL; hr = pIY->QueryInterface(IID_IUnknown, (void**)&pIUknownFromIY); if(SUCCEEDED(hr)) { cout << “equal?” ; if(pIUknownFromIY == pIUnknown) { cout << “Yes.” << endl; } else { cout << “No.” << endl; } } //Delete the component delete pIUnknown; return 0; }