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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.

Questions and answers

  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
  66. What is COM aggrigation? answer


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