QPtrDict Class

Qt 3.0.5

previous page next page

QPtrDict Class Reference

The QPtrDict class is a template class that provides a dictionary based on void* keys. More...

#include <qptrdict.h>

Inherits QPtrCollection.

List of all member functions.

Public Members

QPtrDict ( int size = 17 )
QPtrDict ( const QPtrDict<type> & dict )
~QPtrDict ()
QPtrDict<type> & operator= ( const QPtrDict<type> & dict )
virtual uint count () const
uint size () const
bool isEmpty () const
void insert ( void * key, const type * item )
void replace ( void * key, const type * item )
bool remove ( void * key )
type * take ( void * key )
type * find ( void * key ) const
type * operator[] ( void * key ) const
virtual void clear ()
void resize ( uint newsize )
void statistics () const

Important Inherited Members

bool autoDelete () const
void setAutoDelete ( bool enable )

Protected Members

virtual QDataStream & read ( QDataStream & s, QPtrCollection::Item & item )
virtual QDataStream & write ( QDataStream & s, QPtrCollection::Item ) const

Detailed Description

The QPtrDict class is a template class that provides a dictionary based on void* keys.

QPtrDict is implemented as a template class. Define a template instance QPtrDict<X> to create a dictionary that operates on pointers to X (X*).

A dictionary is a collection of key-value pairs. The key is a void* used for insertion, removal and lookup. The value is a pointer. Dictionaries provide very fast insertion and lookup.

Example:

    QPtrDict<char> extra;

    QLineEdit *le1 = new QLineEdit( this );
    le1->setText( "Simpson" );
    QLineEdit *le2 = new QLineEdit( this );
    le2->setText( "Homer" );
    QLineEdit *le3 = new QLineEdit( this );
    le3->setText( "45" );

    extra.insert( le1, "Surname" );
    extra.insert( le2, "Forename" );
    extra.insert( le3, "Age" );

    QPtrDictIterator<char> it( extra ); // See QPtrDictIterator
    for( ; it.current(); ++it )
        cout << it.current() << endl;
    cout << endl;

    if ( extra[le1] ) // Prints "Surname: Simpson"
        cout << extra[le1] << ": " << le1->text() << endl; 
    if ( extra[le2] ) // Prints "Forename: Homer"
        cout << extra[le2] << ": " << le2->text() << endl; 

    extra.remove( le1 ); // Removes le1 from the dictionary
    cout << le1->text() << endl; // Prints "Simpson"

In this example we use a dictionary to add an extra property (a char*) to the line edits we're using.

See QDict for full details, including the choice of dictionary size, and how deletions are handled.

Member Function Documentation

QPtrDict::QPtrDict ( int size = 17 )

Constructs a dictionary using an internal hash array with the size size.

Setting size to a suitably large prime number (equal to or greater than the expected number of entries) makes the hash distribution better and hence the lookup faster.

QPtrDict::QPtrDict ( const QPtrDict<type> & dict )

Constructs a copy of dict.

Each item in dict is inserted into this dictionary. Only the pointers are copied (shallow copy).

QPtrDict::~QPtrDict ()

Removes all items from the dictionary and destroys it.

All iterators that access this dictionary will be reset.

bool QPtrCollection::autoDelete () const

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

void QPtrDict::clear () `[virtual]`

Removes all items from the dictionary.

The removed items are deleted if auto-deletion is enabled.

All dictionary iterators that access this dictionary will be reset.

See also remove(), take() and setAutoDelete().

Reimplemented from QPtrCollection.

uint QPtrDict::count () const `[virtual]`

Returns the number of items in the dictionary.

type * QPtrDict::find ( void * key ) const

Returns the item associated with key, or null if the key does not exist in the dictionary.

This function uses an internal hashing algorithm to optimize lookup.

If there are two or more items with equal keys, then the last item that was inserted will be found.

Equivalent to the [] operator.

Warning: Your application will crash if you call find() on an empty dictionary; you can check with isEmpty() or count(). We don't perform this check for efficiency reasons.

void QPtrDict::insert ( void * key, const type * item )

Inserts the key with the item into the dictionary.

The key does not have to be a unique dictionary key. If multiple items are inserted with the same key, only the last item will be visible.

Null items are not allowed.

bool QPtrDict::isEmpty () const

Returns TRUE if the dictionary is empty; otherwise returns FALSE.

QPtrDict<type> & QPtrDict::operator= ( const QPtrDict<type> & dict )

Assigns dict to this dictionary and returns a reference to this dictionary.

This dictionary is first cleared and then each item in dict is inserted into the dictionary. Only the pointers are copied (shallow copy), unless newItem() has been reimplemented.

type * QPtrDict::operator[] ( void * key ) const

Returns the item associated with key, or null if the key does not exist in the dictionary.

This function uses an internal hashing algorithm to optimize lookup.

If there are two or more items with equal keys, then the last item that was inserted will be found.

Equivalent to the find() function.

Warning: Your application will crash if you call find() on an empty dictionary; you can check with isEmpty() or count(). We don't perform this check for efficiency reasons.

QDataStream & QPtrDict::read ( QDataStream & s, QPtrCollection::Item & item ) `[virtual protected]`

Reads a dictionary item from the stream s and returns a reference to the stream.

The default implementation sets item to 0.

bool QPtrDict::remove ( void * key )

Removes the item associated with key from the dictionary. Returns TRUE if successful, or FALSE if the key does not exist in the dictionary.

If there are two or more items with equal keys, then the last item that was inserted of will be removed.

The removed item is deleted if auto-deletion is enabled.

All dictionary iterators that refer to the removed item will be set to point to the next item in the dictionary traversal order.

See also take(), clear() and setAutoDelete().

void QPtrDict::replace ( void * key, const type * item )

If the dictionary has key key, this key's item is replaced with item. If the dictionary doesn't contain key key, item is inserted into the dictionary using key key.

Null items are not allowed.

Equivalent to

    QPtrDict<char> dict;
        ...
    if ( dict.find( key ) )
        dict.remove( key );
    dict.insert( key, item );

If there are two or more items with equal keys, then the last inserted of these will be replaced.

void QPtrDict::resize ( uint newsize )

Changes the size of the hash table to newsize. The contents of the dictionary are preserved, but all iterators on the dictionary become invalid.

void QPtrCollection::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.

uint QPtrDict::size () const

Returns the size of the internal hash table (as specified in the constructor).

void QPtrDict::statistics () const

Debugging-only function that prints out the dictionary distribution using qDebug().

type * QPtrDict::take ( void * key )

Takes the item associated with key out of the dictionary without deleting it (even if auto-deletion is enabled).