COM

C++ IUnknown , C++ (runtime layer) . IUnknown , . C++, C++ , , , .

Visual Basic Java, C++, QueryInterface, AddRef Release. IUnknown . Java QueryInterface :

 public void TryToSnoreAndIgnore(Object obj) {      IPug pug;      try {         pug = (IPug)obj;         // VM calls QueryInterface         // VM   QueryInterface         pug.Snore();      } catch (Throwable ex) {         // ignore method or QI failures         //         QI  }  ICat cat;  try {      cat = (ICat)obj;      // VM calls QueryInterface      // VM   QueryInterface      cat.IgnoreMaster();  } catch (Throwable ex) {      // ignore method or QI failures      //         QI      }  }  

Visual Basic . , , (VM) Visual Basic QueryInterface :

 Sub TryToSnoreAndIgnore(obj as Object)  On Error Resume Next  ' ignore errors  '      Dim pug as IPug  Set pug = obj  ' VM calls QueryInterface  ' VM   QueryInterface  If Not (pug is Nothing) Then    pug.Snore  End if  Dim cat as ICat  Set cat = obj  ' VM calls QueryInterface  ' VM   QueryInterface  If Not (cat is Nothing) Then    cat.IgnoreMaster  End if End Sub  

, Java, Visual Basic, QueryInterface . AddRef Release, .

, C++, , . (raw) IUnknown. :

1. Add/Release .
2. , ( ) .
3. C++ QueryInterface.
4. ( ) .

. - , , , . Visual C++ 5.0, , ( MSC, ATL, Direct-to-COM), , . 1995 1996 "C++ Report" , ¹. , , - , . , , . , SmartInterface, (template) : C++ IID. IUnknown :

 #include "smartif.h"  void TryToSnoreAndIgnore(/* [in] */ IUnknown *pUnk)  {        // copy constructor calls QueryInterface        //       QueryInterface      SmartInterface<IPug, &IID_IPug> pPug = pUnk;      if (pPug)        // typecast operator returns null-ness        //                    pPug->Snore();        // operator-> returns safe raw ptr        //   ->              // copy constructor calls QueryInterface        //       QueryInterface      SmartInterface<ICat, &IID_ICat> pCat = pUnk;      if (pCat)        // typecast operator returns null-ness        //                    pCat->IgnoreMaster();        // operator-> returns safe raw ptr        //   ->              // destructors release held pointers on leaving scope        //                  //          }  

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¹ http:/www.develop.com/dbox/cxx/InterfacePtr.htm http://www.develop.com/dbox/cxx/SmartPtr.htm.