combase.h

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//------------------------------------------------------------------------------
// File: ComBase.h
//
// Desc: DirectShow base classes - defines a class hierarchy for creating
//       COM objects.
//
// Copyright (c) 1992-2001 Microsoft Corporation.  All rights reserved.
//------------------------------------------------------------------------------


/*

a. Derive your COM object from CUnknown

b. Make a static CreateInstance function that takes an LPUNKNOWN, an HRESULT *
   and a TCHAR *. The LPUNKNOWN defines the object to delegate IUnknown calls
   to. The HRESULT * allows error codes to be passed around constructors and
   the TCHAR * is a descriptive name that can be printed on the debugger.

   It is important that constructors only change the HRESULT * if they have
   to set an ERROR code, if it was successful then leave it alone or you may
   overwrite an error code from an object previously created.

   When you call a constructor the descriptive name should be in static store
   as we do not copy the string. To stop large amounts of memory being used
   in retail builds by all these static strings use the NAME macro,

   CMyFilter = new CImplFilter(NAME("My filter"),pUnknown,phr);
   if (FAILED(hr)) {
       return hr;
   }

   In retail builds NAME(_x_) compiles to NULL, the base CBaseObject class
   knows not to do anything with objects that don't have a name.

c. Have a constructor for your object that passes the LPUNKNOWN, HRESULT * and
   TCHAR * to the CUnknown constructor. You can set the HRESULT if you have an
   error, or just simply pass it through to the constructor.

   The object creation will fail in the class factory if the HRESULT indicates
   an error (ie FAILED(HRESULT) == TRUE)

d. Create a FactoryTemplate with your object's class id and CreateInstance
   function.

Then (for each interface) either

Multiple inheritance

1. Also derive it from ISomeInterface
2. Include DECLARE_IUNKNOWN in your class definition to declare
   implementations of QueryInterface, AddRef and Release that
   call the outer unknown
3. Override NonDelegatingQueryInterface to expose ISomeInterface by
   code something like

     if (riid == IID_ISomeInterface) {
         return GetInterface((ISomeInterface *) this, ppv);
     } else {
         return CUnknown::NonDelegatingQueryInterface(riid, ppv);
     }

4. Declare and implement the member functions of ISomeInterface.

or: Nested interfaces

1. Declare a class derived from CUnknown
2. Include DECLARE_IUNKNOWN in your class definition
3. Override NonDelegatingQueryInterface to expose ISomeInterface by
   code something like

     if (riid == IID_ISomeInterface) {
         return GetInterface((ISomeInterface *) this, ppv);
     } else {
         return CUnknown::NonDelegatingQueryInterface(riid, ppv);
     }

4. Implement the member functions of ISomeInterface. Use GetOwner() to
   access the COM object class.

And in your COM object class:

5. Make the nested class a friend of the COM object class, and declare
   an instance of the nested class as a member of the COM object class.

   NOTE that because you must always pass the outer unknown and an hResult
   to the CUnknown constructor you cannot use a default constructor, in
   other words you will have to make the member variable a pointer to the
   class and make a NEW call in your constructor to actually create it.

6. override the NonDelegatingQueryInterface with code like this:

     if (riid == IID_ISomeInterface) {
         return m_pImplFilter->
            NonDelegatingQueryInterface(IID_ISomeInterface, ppv);
     } else {
         return CUnknown::NonDelegatingQueryInterface(riid, ppv);
     }

You can have mixed classes which support some interfaces via multiple
inheritance and some via nested classes

*/

#ifndef __COMBASE__
#define __COMBASE__
/* Version of IUnknown that is renamed to allow a class to support both
   non delegating and delegating IUnknowns in the same COM object */

#define CheckPointer(p,ret) {if((p)==NULL) return (ret);}
#ifdef DEBUG
 #define NAME(x) TEXT(x)
#else
 #define NAME(_x_) ((TCHAR *) NULL)
#endif

#ifndef INONDELEGATINGUNKNOWN_DEFINED
DECLARE_INTERFACE(INonDelegatingUnknown)
{
 STDMETHOD(NonDelegatingQueryInterface) (THIS_ REFIID, LPVOID *) PURE;
 STDMETHOD_(ULONG, NonDelegatingAddRef)(THIS) PURE;
 STDMETHOD_(ULONG, NonDelegatingRelease)(THIS) PURE;
};
#define INONDELEGATINGUNKNOWN_DEFINED
#endif

typedef INonDelegatingUnknown *PNDUNKNOWN;


/* This is the base object class that supports active object counting. As
   part of the debug facilities we trace every time a C++ object is created
   or destroyed. The name of the object has to be passed up through the class
   derivation list during construction as you cannot call virtual functions
   in the constructor. The downside of all this is that every single object
   constructor has to take an object name parameter that describes it. */

class CBaseObject
 {

 private:

  /* Disable the copy constructor and assignment by default so you will get
     compiler errors instead of unexpected behaviour if you pass objects
     by value or assign objects. */
  CBaseObject(const CBaseObject& objectSrc);          // no implementation
  void operator=(const CBaseObject& objectSrc);       // no implementation

 protected:

 public:

  /* These increment and decrement the number of active objects. */

  CBaseObject(const TCHAR *pName);

  ~CBaseObject();

  /* Call this to find if there are any CUnknown derived objects active. */

 };



#ifdef  _MSC_VER
 #if _MSC_VER>=1100
  #define AM_NOVTABLE __declspec(novtable)
 #else
  #define AM_NOVTABLE
 #endif
#else
 #define AM_NOVTABLE
#endif  // MSC_VER

/* An object that supports one or more COM interfaces will be based on
   this class. It supports counting of total objects for DLLCanUnloadNow
   support, and an implementation of the core non delegating IUnknown. */

class AM_NOVTABLE CUnknown : public INonDelegatingUnknown,
   public CBaseObject
 {
 private:
  const LPUNKNOWN m_pUnknown; // Owner of this object.

 protected:                   // So we can override NonDelegatingRelease()
  volatile LONG m_cRef;       // Number of reference counts

 public:

  CUnknown(const TCHAR *pName, LPUNKNOWN pUnk);
  virtual ~CUnknown()
  {}
  ;

  /* This is redundant, just use the other constructor
     as we never touch the HRESULT in this anyway. */
  CUnknown(TCHAR *pName, LPUNKNOWN pUnk,HRESULT *phr);

  // Return the owner of this object.

  LPUNKNOWN GetOwner() const
   {
    return m_pUnknown;
   };

  /* Called from the class factory to create a new instance, it is
     pure virtual so it must be overriden in your derived class. */

  // static CUnknown *CreateInstance(LPUNKNOWN, HRESULT *)

  // Non delegating unknown implementation.

  STDMETHODIMP NonDelegatingQueryInterface(REFIID, void **);
  STDMETHODIMP_(ULONG) NonDelegatingAddRef();
  STDMETHODIMP_(ULONG) NonDelegatingRelease();
 };

/* Return an interface pointer to a requesting client
   performing a thread safe AddRef as necessary. */

STDAPI GetInterface(LPUNKNOWN pUnk, void **ppv);

// A function that can create a new COM object.

typedef CUnknown *(CALLBACK *LPFNNewCOMObject)(LPUNKNOWN pUnkOuter, HRESULT *phr);

/* A function (can be NULL) which is called from the DLL entrypoint
   routine for each factory template:

   bLoading - TRUE on DLL load, FALSE on DLL unload
   rclsid   - the m_ClsID of the entry */
typedef void (CALLBACK *LPFNInitRoutine)(BOOL bLoading, const CLSID *rclsid);

#define DECLARE_IUNKNOWN                                    \
    STDMETHODIMP QueryInterface(REFIID riid, void **ppv) {  \
        return GetOwner()->QueryInterface(riid,ppv);        \
    };                                                      \
    STDMETHODIMP_(ULONG) AddRef() {                         \
        return GetOwner()->AddRef();                        \
    };                                                      \
    STDMETHODIMP_(ULONG) Release() {                        \
        return GetOwner()->Release();                       \
    };

#endif // __COMBASE__