Version: 3.1.1

#include <wx/object.h>

Detailed Description

template<class T>
class wxObjectDataPtr< T >

This is an helper template class primarily written to avoid memory leaks because of missing calls to wxRefCounter::DecRef() and wxObjectRefData::DecRef().

Despite the name this template can actually be used as a smart pointer for any class implementing the reference counting interface which only consists of the two methods T::IncRef() and T::DecRef().

The difference to wxSharedPtr<T> is that wxObjectDataPtr<T> relies on the reference counting to be in the class pointed to, where instead wxSharedPtr<T> implements the reference counting itself.

Below is an example illustrating how to implement reference counted data using wxRefCounter and wxObjectDataPtr<T> with copy-on-write semantics.

Example

class MyCarRefData: public wxRefCounter
{
public:
MyCarRefData( int price = 0 ) : m_price(price) { }
MyCarRefData( const MyCarRefData& data ) : m_price(data.m_price) { }
void SetPrice( int price ) { m_price = price; }
int GetPrice() const { return m_price; }
protected:
int m_price;
};
class MyCar
{
public:
// initializes this MyCar assigning to the
// internal data pointer a new instance of MyCarRefData
MyCar( int price = 0 ) : m_data( new MyCarRefData(price) )
{
}
MyCar& operator =( const MyCar& tocopy )
{
// shallow copy: this is just a fast copy of pointers; the real
// memory-consuming data which typically is stored inside
// MyCarRefData is not copied here!
m_data = tocopy.m_data;
return *this;
}
bool operator == ( const MyCar& other ) const
{
if (m_data.get() == other.m_data.get())
return true; // this instance and the 'other' one share the
// same MyCarRefData data...
return (m_data.GetPrice() == other.m_data.GetPrice());
}
void SetPrice( int price )
{
// make sure changes to this class do not affect other instances
// currently sharing our same refcounted data:
UnShare();
m_data->SetPrice( price );
}
int GetPrice() const
{
return m_data->GetPrice();
}
wxObjectDataPtr<MyCarRefData> m_data;
protected:
void UnShare()
{
if (m_data->GetRefCount() == 1)
return;
m_data.reset( new MyCarRefData( *m_data ) );
}
};

Library:  wxBase
Category:  Runtime Type Information (RTTI), Smart Pointers
See also
wxObject, wxObjectRefData, Reference Counting, wxSharedPtr<T>, wxScopedPtr<T>, wxWeakRef<T>

Public Member Functions

 wxObjectDataPtr (T *ptr=NULL)
 Constructor. More...
 
 wxObjectDataPtr (const wxObjectDataPtr< T > &tocopy)
 This copy constructor increases the count of the reference counted object to which tocopy points and then this class will point to, as well. More...
 
 ~wxObjectDataPtr ()
 Decreases the reference count of the object to which this class points. More...
 
T * get () const
 Gets a pointer to the reference counted object to which this class points. More...
 
void reset (T *ptr)
 Reset this class to ptr which points to a reference counted object and calls T::DecRef() on the previously owned object. More...
 
 operator unspecified_bool_type () const
 Conversion to a boolean expression (in a variant which is not convertable to anything but a boolean expression). More...
 
T & operator* () const
 Returns a reference to the object. More...
 
T * operator-> () const
 Returns a pointer to the reference counted object to which this class points. More...
 
wxObjectDataPtr< T > & operator= (const wxObjectDataPtr< T > &tocopy)
 Assignment operator. More...
 
wxObjectDataPtr< T > & operator= (T *ptr)
 Assignment operator. More...
 

Constructor & Destructor Documentation

template<class T >
wxObjectDataPtr< T >::wxObjectDataPtr ( T *  ptr = NULL)

Constructor.

ptr is a pointer to the reference counted object to which this class points. If ptr is not NULL T::IncRef() will be called on the object.

template<class T >
wxObjectDataPtr< T >::wxObjectDataPtr ( const wxObjectDataPtr< T > &  tocopy)

This copy constructor increases the count of the reference counted object to which tocopy points and then this class will point to, as well.

template<class T >
wxObjectDataPtr< T >::~wxObjectDataPtr ( )

Decreases the reference count of the object to which this class points.

Member Function Documentation

template<class T >
T* wxObjectDataPtr< T >::get ( ) const

Gets a pointer to the reference counted object to which this class points.

template<class T >
wxObjectDataPtr< T >::operator unspecified_bool_type ( ) const

Conversion to a boolean expression (in a variant which is not convertable to anything but a boolean expression).

If this class contains a valid pointer it will return true, if it contains a NULL pointer it will return false.

template<class T >
T& wxObjectDataPtr< T >::operator* ( ) const

Returns a reference to the object.

If the internal pointer is NULL this method will cause an assert in debug mode.

template<class T >
T* wxObjectDataPtr< T >::operator-> ( ) const

Returns a pointer to the reference counted object to which this class points.

If this the internal pointer is NULL, this method will assert in debug mode.

template<class T >
wxObjectDataPtr<T>& wxObjectDataPtr< T >::operator= ( const wxObjectDataPtr< T > &  tocopy)

Assignment operator.

template<class T >
wxObjectDataPtr<T>& wxObjectDataPtr< T >::operator= ( T *  ptr)

Assignment operator.

template<class T >
void wxObjectDataPtr< T >::reset ( T *  ptr)

Reset this class to ptr which points to a reference counted object and calls T::DecRef() on the previously owned object.