Question

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

Important Inherited Members

• bool autoDelete () const
• void setAutoDelete ( boolenable )

Protected Members

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

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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.

See also QPtrDictIterator, QDict, QAsciiDict, QIntDict, Collection Classes, Collection Classes and Non-GUI Classes.

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Member Function Documentation

QPtrDict::QPtrDict ( intsize = 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 ( constQPtrDict<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.

See also setAutoDelete().

bool QPtrCollection::autoDelete () const

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

See also setAutoDelete().

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.

See also isEmpty().

Reimplemented from QPtrCollection.

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.

See also operator[]().

void QPtrDict::insert ( void*key, consttype*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.

See also replace().

bool QPtrDict::isEmpty () const

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

See also count().

QPtrDict<type>& QPtrDict::operator= ( constQPtrDict<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.

See also find().

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.

See also write().

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, consttype*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.

See also insert().

void QPtrDict::resize ( uintnewsize )

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 ( boolenable )

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().

Examples: grapher/grapher.cpp, scribble/scribble.cpp and table/bigtable/main.cpp.

uint QPtrDict::size () const

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

See also count().

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).

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

Returns a pointer to the item taken out, or null if the key does not exist in the dictionary.

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

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

QDataStream& QPtrDict::write ( QDataStream&s, QPtrCollection::Item ) const [virtual protected]

Writes a dictionary item to the stream s and returns a reference to the stream.

See also read().