Qt Reference Documentation

Q3PtrCollection Class Reference

The Q3PtrCollection class is the base class of most pointer-based Qt collections. More...

 #include <Q3PtrCollection>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

Inherited by: Q3AsciiCache, Q3AsciiDict, Q3Cache, Q3Dict, Q3IntCache, Q3IntDict, Q3PtrDict, Q3PtrList, Q3PtrQueue, Q3PtrStack, and Q3PtrVector.

Note: All functions in this class are reentrant.

Public Types

typedef Item

Public Functions

bool autoDelete () const
virtual void clear () = 0
virtual uint count () const = 0
void setAutoDelete ( bool enable )

Protected Functions

Q3PtrCollection ()
Q3PtrCollection ( const Q3PtrCollection & source )
virtual ~Q3PtrCollection ()
virtual void deleteItem ( Item d ) = 0
virtual Item newItem ( Item d )

Detailed Description

The Q3PtrCollection class is the base class of most pointer-based Qt collections.

The Q3PtrCollection class is an abstract base class for the Qt collection classes QDict, Q3PtrList, etc.

A Q3PtrCollection only knows about the number of objects in the collection and the deletion strategy (see setAutoDelete()).

A collection is implemented using the Item (generic collection item) type, which is a void*. The template classes that create the real collections cast the Item to the required type.

Member Type Documentation

typedef Q3PtrCollection::Item

This type is the generic "item" in a Q3PtrCollection.

Member Function Documentation

Q3PtrCollection::Q3PtrCollection () [protected]

Constructs a collection. The constructor is protected because Q3PtrCollection is an abstract class.

Q3PtrCollection::Q3PtrCollection ( const Q3PtrCollection & source ) [protected]

Constructs a copy of source with autoDelete() set to false. The constructor is protected because Q3PtrCollection is an abstract class.

Note that if source has autoDelete turned on, copying it will risk memory leaks, reading freed memory, or both.

Q3PtrCollection::~Q3PtrCollection () [virtual protected]

Destroys the collection. The destructor is protected because Q3PtrCollection is an abstract class.

bool Q3PtrCollection::autoDelete () const

Returns the setting of the auto-delete option. The default is false.

See also setAutoDelete().

void Q3PtrCollection::clear () [pure virtual]

Removes all objects from the collection. The objects will be deleted if auto-delete has been enabled.

See also setAutoDelete().

uint Q3PtrCollection::count () const [pure virtual]

Returns the number of objects in the collection.

void Q3PtrCollection::deleteItem ( Item d ) [pure virtual protected]

Reimplement this function if you want to be able to delete items.

Deletes an item that is about to be removed from the collection.

This function has to reimplemented in the collection template classes, and should only delete item d if auto-delete has been enabled.

Warning: If you reimplement this function you must also reimplement the destructor and call the virtual function clear() from your destructor. This is due to the way virtual functions and destructors work in C++: Virtual functions in derived classes cannot be called from a destructor. If you do not do this, your deleteItem() function will not be called when the container is destroyed.

See also newItem() and setAutoDelete().

Item Q3PtrCollection::newItem ( Item d ) [virtual protected]

Virtual function that creates a copy of an object that is about to be inserted into the collection.

The default implementation returns the d pointer, i.e. no copy is made.

This function is seldom reimplemented in the collection template classes. It is not common practice to make a copy of something that is being inserted.

See also deleteItem().

void Q3PtrCollection::setAutoDelete ( bool enable )

Sets the collection to auto-delete its contents if enable is true and to never delete them if enable is false.

If auto-deleting is turned on, all the items in a collection are deleted when the collection itself is deleted. This is convenient if the collection has the only pointer to the items.

The default setting is false, for safety. If you turn it on, be careful about copying the collection - you might find yourself with two collections deleting the same items.

Note that the auto-delete setting may also affect other functions in subclasses. For example, a subclass that has a remove() function will remove the item from its data structure, and if auto-delete is enabled, will also delete the item.

See also autoDelete().