interface
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The document discusses interfaces in COM. It explains that interfaces allow invoking functions of COM objects indirectly using virtual function techniques. It shows how to define a pure abstract interface class and have implementation classes inherit the interface. Clients can call interface methods without knowing the underlying implementation class. Later sections discuss adding multiple interfaces to a class, querying for interfaces, and how a client can load and use a COM server from a DLL.
interface
- 1. 1 INTERFACE in COM nonezerok@gmail.com 저자의 동의 없이 본 문서 일부 또는 전체의 무단복제를 불허합니다.
- 2. 2 a.exe b.dll it is possible extern “C” void __stdcall Fx(); Dynamic Link Library (Local Procedure Call)
- 3. 3 a.exe b.dll Is it possible ? Invoking functions of an Object
- 4. 4 a.exe b.dll No !!! encapsulated and information hidden Invoking functions of an Object
- 5. 5 a.exe b.dll interface however, How to achieve it ? make a window; call it an interface
- 6. 6 Virtual Function Technique class A { int d1; int show() { cout << “A” << endl; }; } ; class B: public A { int d2; int show() { cout << “B” << endl; }; } ; void main() { A a, *pA; B b, *pB; pA = &b; pA‐>show(); // A or B ? What is your expectation ? }
- 7. 7 class A { int d1; virtual int show() { cout << “A” << endl; }; } ; class B: public A { int d2; int show() { cout << “B” << endl; }; } ; void main() { A a, *pA; B b, *pB; pA = &b; pA‐>show(); // before and after adding virtual cout << sizeof(a) << endl; } How about adding another virtual function ? virtual int draw() in the class A
- 8. 8 vPtr d1 d2 A::show() B::show() A::draw() B::draw() pA (&b) virtual function table dynamic binding Note: we can invoke B’s functions using A
- 9. 9 Conceptual View of Interface a.exe b.dll public
- 10. 10 struct IX // pure abstract class (here, public class) { virtual void __stdcall Fx1() = 0; // pure virtual function virtual void __stdcall Fx2() = 0; // abstract class }; class CA: public IX { void __stdcall Fx1() { cout << “Fx1” << endl; }; void __stdcall Fx2() { cout << “Fx2” << endl; }; }; void main() { CA* pA = new CA; IX* pX = (IX*)pA; pX‐>Fx1(); delete pA; } • Using the virtual function technique, we can indirectly invoke the function of a COM object • Public Pure Abstract Class Definition of Interface
- 11. 11 #define interface struct interface IX // pure abstract class (here, public class) { virtual void __stdcall Fx1() = 0; // pure virtual function virtual void __stdcall Fx2() = 0; // abstract class }; class CA: public IX { void __stdcall Fy1() { cout << “Fy1” << endl; }; void __stdcall Fy2() { cout << “Fy2” << endl; }; }; void main() { CA* pA = new CA; IX* pX = (IX*)pA; pX‐>Fx1(); delete pA; } Can this main function be a client-side code ?
- 12. 12 interface IY { virtual void __stdcall Fy1() = 0; virtual void __stdcall Fy2() = 0; }; class CA: public IX, public IY { void __stdcall Fy1() { cout << “Fy1” << endl; }; void __stdcall Fy2() { cout << “Fy2” << endl; }; }; IX* CreateInstance() { CA* pA = new CA; return pA; } void main() { IX* pX = CreateInstance(); pX‐>Fx1(); IY* pY = (IY*)pX; // ? pY‐>Fy1(); // ? delete pX; } What for adding another interface ?
- 13. 13 interface IU { }; interface IX: IU { … }; interface IY: IU { … }; class CA: public IX, public IY { void __stdcall Fx1() { cout << “Fx1” << endl; }; void __stdcall Fx1() { cout << “Fx2” << endl; }; void __stdcall Fy1() { cout << “Fy1” << endl; }; void __stdcall Fy2() { cout << “Fy2” << endl; }; } ; IU* CreateInstance() { CA* pA = new CA; return (IX*)pA; } void main() { IU* pU = CreateInstance(); IX* pX = (IX*)pU; pX‐>Fx1(); // ? IY* pY = (IY*)pU; pY‐>Fy1(); // ? delete pX; }
- 14. 14 interface IU { virtual bool __stdcall QI(int id, void** ppv) = 0; }; interface IX: IU { … }; interface IY: IU { … }; class CA: public IX, public IY { bool __stdcall QI(int id, void** ppv) { if (id == IID_IX) *ppv = (IX*) this; else if (id == IID_IY) *ppv = (IY*) this; else { *ppv = NULL; return false; }; return true; } }; void main() { IU* pU = CreateInstance(); IX* pX; pU‐>QI(IID_IX, (void**)&pX); pX‐>Fx1(); IY* pY; pU‐>QI(IID_IY, (void**)&pY); pY‐>Fy1(); delete pX; }
- 15. 15 Client for DLL Server typedef IUnknown* (*FUNCPTR)(); void main() { HINSTANCE hDll; hDll = LoadLibary(“d:comserver.dll”); FUNCPTR CreateInstance = (FUNCPTR)::GetProcAddress (hDll, ʺCreateInstanceʺ); IU* pU = CreateInstance(); IX* pX; pU‐>QI(IID_IX, (void**)&pX); pX‐>Fx1(); IY* pY; pU‐>QI(IID_IY, (void**)&pY); pY‐>Fy1(); delete pX; FreeLibrary(hDll); } path If the path is changed ?