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COM/DCOM Programming: 66 Exam and interview questions on COM/DCOM/ActiveX for developers/learners. Click on the link to get the detailed explanations. One you visit any answer you can navigate through next and previous link to jump from one answer to another. You can also select index to come back to this index page. Please provide us the rating and feedbacks of our questions and answers.

Topic Discussed: OLE, COM, C++ exported class, interface based programming, IDL, ODL, COM class, QueryInterface(), AddRef() and Release() function? HRESULT, wrapper class, BSTR, factory class, IClassFactory, CreateInstance(), LockServer(), entry and exit point, self-registration and unregistration, CLSID, GUID, UUID, APPID, InProc (In Process) and Out-Of-Process, proxy/stub scheleton, help/guide line string, [in], [out], [in,out] and [out,retval], co-class, smart pointer, Marshalling, TypeLibrary, IUnknown, IDispatch, GetIDsofName(), Invoke(), Automation, SAFE ARRAY, enum types, callback, connectable object, Sink object, Apartment, STA, MTA, Single and Multi-Threaded Apartment, ActiveX, IEnumXXX, in-bound and out-bound interface, out-of process, SINGLEUSE, MULTIUSE, MULTI_SEPARATE, SUSPENDED, SURROGATE, COM aggrigation.

1) What is Object Linking and Embedding? answer

2) What is Component Object Model? answer

3) What are the advantages of using COM object over using C++ exported class? answer

4) What are the advantages of interface based programming? answer

5) What is Interface Definition Language or IDL? answer

6) What is Object Definition Language? answer

7) How can I define a Interface? answer

8) What is the base class of all COM class? Define its prototype. answer

9) What is the utility of QueryInterface() function in IUnknown interface? answer

10) What is the utility of AddRef() and Release() function? answer

11) Does AddRef() is called by client? answer

12) Who allocates memory for a COM object and where its construction get called? answer

13) What is HRESULT? Why all function is COM returns HRESULT? How do we come to know the function returns a success or failure? If failure what is the reson behind? How function returns a logical value? answer

14) What is a wrapper class? answer

15) How can I implement a wrapper class? answer

16) What is BSTR? How it differs from an array of unicode wchar_t? answer

17) What is a factory class? answer

18) What is the definition of a IClassFactory interface? answer

19) What is the utility of CreateInstance() function in IClassFactory? answer

20) What is the utility of LockServer()? answer

21) What are the entry and exit point routine of COM DLL module? answer

22) How a COM DLL can provide self-registration and deregistration? answer

23) What is CLSID, GUID, UUID, APPID ? How it is determined? answer

24) What is InProc (In Process) and Out-Of-Process COM server? answer

25) Write steps to create a com client? answer

26) How do I define a method in an interface using IDL? answer

27) What is the difference between a COM server written solely in C++ (no IDL) and using C++ and IDL? answer

28) What are the output of MIDL compilation of an IDL file? answer

29) What is proxy/stub scheleton in COM client and server programming? answer

30) How can I add some help/guide line string in the definition of a method to help client to understand the functionality of the method? answer

31) What is [in], [out], [in,out] and [out,retval] parameters? answer

32) Why out parameters are always pointer to pointer? answer

33) Who frees OUT parameters? answer

34) How BSTRs are allocated and deallocated? answer

35) How can I convert ASCII string to BSTR using ATL framework and Win32 APIs? answer

36) What is a co-class in a COM server? answer

37) What is smart pointer? What is the advantages of using it? How can I generate smart pointer classes from a COM server? What are the file names smart pointers are defined and where those are implemented? answer

38) What is Marshalling in COM? answer

39) What is TypeLibrary? answer

40) How can I write an Interface that supports type info? answer

41) What is the definition of IDispatch? answer

42) How IDispatch supports VB, JAVA, script enabled object? answer

43) What is ID binding? What is the utility of GetIDsofName() function in IDispatch()? answer

44) How Invoke() method is called using Automation? answer

45) What is Automation in COM? answer

46) What is variant in Automation? answer

47) How arrays are implemented in COM/Automation? answer

48) How SAFE ARRAY differs from normal array? answer

49) How enum types are supported in COM? answer

50) What is a callback function in COM? answer

51) How callback function are implemented in COM? answer

52) What is connectable object in COM? How to implement callback event using connection point and what is the advantage? answer

53) What is a Sink object in COM? answer

54) What is an COM Apartment? answer

55) What is Single Threaded Apartment or STA? answer

56) What is Multi-Threaded Apartment or MTA? What is the basic difference between MTA enabled and STA com server code? answer

57) What is an ActiveX object? answer

58) What is IEnumXXX interface and how it is used? answer

59) How an array of fixed length data are passed in method? answer

60) Distinguish between an in-bound and out-bound interface? answer

61) What is a co-class in IDL? What is a default co-class in VB? answer

62) What is the difference between a coclass and Interface in IDL? answer

63) What is the easiest way to register a type library programatically? answer

64) How a out-of process COM EXE register itself to Service Control Manager(SCM)? answer

65) What is the meaning of SINGLEUSE, MULTIUSE, MULTI_SEPARATE, SUSPENDED, SURROGATE in COM Exe? answer

66) What is COM aggrigation? answer

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