include/wx/msw/private/comptr.h

   1 ///////////////////////////////////////////////////////////////////////////////
   2 // Name:        wx/msw/private/comptr.h
   3 // Purpose:     Smart pointer for COM interfaces.
   4 // Author:      PB
   5 // Created:     2012-04-16
   6 // RCS-ID:      $Id$
   7 // Copyright:   (c) 2012 wxWidgets team
   8 // Licence:     wxWindows licence
   9 ///////////////////////////////////////////////////////////////////////////////
  10
  11 #ifndef _WX_MSW_PRIVATE_COMPTR_H_
  12 #define _WX_MSW_PRIVATE_COMPTR_H_
  13
  14 // ----------------------------------------------------------------------------
  15 // wxCOMPtr: A minimalistic smart pointer for use with COM interfaces.
  16 // ----------------------------------------------------------------------------
  17
  18 template <class T>
  19 class wxCOMPtr
  20 {
  21 public:
  22     typedef T element_type;
  23
  24     wxCOMPtr()
  25         : m_ptr(NULL)
  26     {
  27     }
  28
  29     wxEXPLICIT wxCOMPtr(T* ptr)
  30         : m_ptr(ptr)
  31     {
  32         if ( m_ptr )
  33             m_ptr->AddRef();
  34     }
  35
  36     wxCOMPtr(const wxCOMPtr& ptr)
  37         : m_ptr(ptr.get())
  38     {
  39         if ( m_ptr )
  40             m_ptr->AddRef();
  41     }
  42
  43     ~wxCOMPtr()
  44     {
  45         if ( m_ptr )
  46             m_ptr->Release();
  47     }
  48
  49     void reset(T* ptr = NULL)
  50     {
  51         if ( m_ptr != ptr)
  52         {
  53             if ( ptr )
  54                 ptr->AddRef();
  55             if ( m_ptr )
  56                 m_ptr->Release();
  57             m_ptr = ptr;
  58         }
  59     }
  60
  61     wxCOMPtr& operator=(const wxCOMPtr& ptr)
  62     {
  63         reset(ptr.get());
  64         return *this;
  65     }
  66
  67     wxCOMPtr& operator=(T* ptr)
  68     {
  69         reset(ptr);
  70         return *this;
  71     }
  72
  73     operator T*() const
  74     {
  75         return m_ptr;
  76     }
  77
  78     T& operator*() const
  79     {
  80         return *m_ptr;
  81     }
  82
  83     T* operator->() const
  84     {
  85         return m_ptr;
  86     }
  87
  88     // It would be better to forbid direct access completely but we do need
  89     // for QueryInterface() and similar functions, so provide it but it can
  90     // only be used to initialize the pointer, not to modify an existing one.
  91     T** operator&()
  92     {
  93         wxASSERT_MSG(!m_ptr,
  94                      wxS("Can't get direct access to initialized pointer"));
  95
  96         return &m_ptr;
  97     }
  98
  99     T* get() const
 100     {
 101         return m_ptr;
 102     }
 103
 104     bool operator<(T* ptr) const
 105     {
 106         return get() < ptr;
 107     }
 108
 109 private:
 110     T* m_ptr;
 111 };
 112
 113 // Define a helper for the macro below: we just need a function taking a
 114 // pointer and not returning anything to avoid warnings about unused return
 115 // value of the cast in the macro itself.
 116 namespace wxPrivate { void PPV_ARGS_CHECK(void*) { } }
 117
 118 // Takes the interface name and a pointer to a pointer of the interface type
 119 // and expands into the IID of this interface and the same pointer but after a
 120 // type-safety check.
 121 //
 122 // This is similar to the standard IID_PPV_ARGS macro but takes the pointer
 123 // type instead of relying on the non-standard Microsoft __uuidof().
 124 #define wxIID_PPV_ARGS(IType, pType) \
 125     IID_##IType, \
 126     (wxPrivate::PPV_ARGS_CHECK(static_cast<IType*>(*pType)), \
 127      reinterpret_cast<void**>(pType))
 128
 129 #endif // _WX_MSW_PRIVATE_COMPTR_H_
 130