EQuestionAnswers.com Computer/Electronics Questions and Answers
C, C++, VC++, COM/DCOM, DLL and more
#Login #Sign up  Facebook Twitter TGoogle+
 

#Previous question #Index of COM/DCOM Questions #Next question

IUnknown::QueryInterface

QueryInterface() is used to obtain an interface pointer of an another class from the exiting interface pointer.
Returns a pointer to a specified interface on an object to which a client currently holds an interface pointer. This function must call IUnknown::AddRef on the pointer it returns.

HRESULT QueryInterface(
  REFIID iid,        //Identifier of the requested interface
  void ** ppvObject  //Address of output variable that receives the
                     //interface pointer requested in iid
);

Parameters

  • iid - [in] Identifier of the interface being requested.
  • ppvObject - [out] Address of pointer variable that receives the interface pointer requested in riid. Upon successful return, *ppvObject contains the requested interface pointer to the object. If the object does not support the interface specified in iid, *ppvObject is set to NULL.

Return Value

  • S_OK if the interface is supported, E_NOINTERFACE if not.

QueryInterface source

STDMETHODIMP CMathLib::QueryInterface(REFIID  iid, LPVOID* ppvObject)
{ 
  if ( iid == IID_IUnknown) {
    *ppvObject = dynamic_cast( this );
  } else 
  if ( iid == IID_IDispatch) {
    *ppvObject = dynamic_cast( this );
  } else
  if ( iid == IID_IMathLib) {
    *ppvObject = dynamic_cast( this );
  }else {
    // It didn't match an interface
    *ppvObject = NULL;
    return E_NOINTERFACE;
  }
  return S_OK;
}

You have viewed 1 page out of 66. Your COM/DCOM learning is 0.00% complete. Login to check your learning progress.

 Vote 0

Similar topics related to this section

# COM DCOM Interview Questions and Answers :: ALL Interview .com
# COM DCOM - COM DCOM Interview Questions
# COM interview questions | TechInterviews
# COM Interview Questions - CodeProject
# Com Dcom Interview Questions - Com and Dcom in Asp Net
# ATL Interview Questions and Answers :: ALL Interview .com
# ActiveX Interview Questions and Answers :: ALL Interview .com

* #1 webmaster Mon 28 Apr/2014 18:21:40(GMT)  Like 0 Unlike 0

Dear Users,

We are pleased to inform you that a forum/blog has been incorporated with www.mybestnotes.co.in. You are welcomed to add your comments, requests, codes, solutions and feedback to it. Please login(if already a member) or signup(for free) to avail to this facility.

Regards,
Webmaster

Your message goes here:

Name:Guest
Email:anonymous@unknown.com
My Post:*
Secutiry Code: ******  *
Preview this compose before posting this in discussion forum.
 
Note:
  1. Use [Sxx] code to show smiles. Example [S02]
  2. Use [URL ], example [URL http://www.google.com/]
  3. To display code or un formatted text use [CODE] [/CODE]. Example: [CODE] printf("Hello world"); [/CODE]
 [S01]   [S02]   [S03]   [S04]   [S05]   [S06]   [S07]   [S08] 
 [S09]   [S10]   [S11]   [S12]   [S13]   [S14]   [S15]   [S16] 
 [S17]   [S18]   [S19]   [S20]   [S21]   [S22]   [S23]   [S24] 

Note: Only members are allowed, * fields are mandatory.