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# Q3PtrDict Class Reference
[Qt3Support module]

The Q3PtrDict class is a template class that provides a dictionary based on void* keys. More...

     #include <Q3PtrDict>

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.

Inherits Q3PtrCollection.

- List of all members, including inherited members

### Public Functions

- Q3PtrDict ( int size = 17 )
- Q3PtrDict ( const Q3PtrDict<type> & dict )
- ~Q3PtrDict ()
- virtual void clear ()
- virtual uint count () const
- type * find ( void * key ) const
- void insert ( void * key, const type * item )
- bool isEmpty () const
- bool remove ( void * key )
- void replace ( void * key, const type * item )
- void resize ( uint newsize )
- uint size () const
- void statistics () const
- type * take ( void * key )
- Q3PtrDict<type> & operator= ( const Q3PtrDict<type> & dict )
- type * operator[] ( void * key ) const

- 4 public functions inherited from Q3PtrCollection

### Protected Functions

- virtual QDataStream & read ( QDataStream & s, Q3PtrCollection::Item & item )
- virtual QDataStream & write ( QDataStream & s, Q3PtrCollection::Item item ) const

- 2 protected functions inherited from Q3PtrCollection

## Detailed Description

The Q3PtrDict class is a template class that provides a dictionary based on void* keys.

Q3PtrDict is implemented as a template class. Define a template instance Q3PtrDict<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:

     Q3PtrDict<char> fields; // void* keys, char* values

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

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

     Q3PtrDictIterator<char> it( fields );
     for( ; it.current(); ++it )
         cout << it.current() << endl;
     cout << endl;

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

     fields.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 Q3Dict for full details, including the choice of dictionary size, and how deletions are handled.

See also Q3PtrDictIterator, Q3Dict, Q3AsciiDict, and Q3IntDict.

## Member Function Documentation

### Q3PtrDict::Q3PtrDict ( 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 improves lookup performance.

### Q3PtrDict::Q3PtrDict ( const Q3PtrDict<type> & dict )

Constructs a copy of dict.

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

### Q3PtrDict::~Q3PtrDict ()

Removes all items from the dictionary and destroys it.

All iterators that access this dictionary will be reset.

See also setAutoDelete().

### void Q3PtrDict::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.

Reimplemented from Q3PtrCollection.

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

### uint Q3PtrDict::count () const `[virtual]`

Returns the number of items in the dictionary.

Reimplemented from Q3PtrCollection.

See also isEmpty().

### type * Q3PtrDict::find ( void * key ) const

Returns the item associated with key, or 0 if the key does not exist in the dictionary.

If there are two or more items with equal keys, then the most recently inserted item will be found.

Equivalent to operator[].

See also operator[]().

### void Q3PtrDict::insert ( void * key, const type * item )

Inserts the key with the item into the dictionary.

Multiple items can have the same key, in which case only the last item will be accessible using operator[]().

item may not be 0.

See also replace().

### bool Q3PtrDict::isEmpty () const

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

See also count().

### QDataStream & Q3PtrDict::read ( QDataStream & s, Q3PtrCollection::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 Q3PtrDict::remove ( void * key )

Removes the item associated with key from the dictionary. Returns TRUE if successful, i.e. if key is in the dictionary; otherwise returns FALSE.

If there are two or more items with equal keys, then the most recently inserted item 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 Q3PtrDict::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.

item may not be 0.

Equivalent to

     Q3PtrDict<ItemType> dict;
         ...
     if ( dict.find( key ) )
         dict.remove( key );
     dict.insert( key, item );

If there are two or more items with equal keys, then the most recently inserted item will be replaced.

See also insert().

### void Q3PtrDict::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.

### uint Q3PtrDict::size () const

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

See also count().

### void Q3PtrDict::statistics () const

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

### type * Q3PtrDict::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 most recently inserted item will be removed.

Returns a pointer to the item taken out, or 0 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 & Q3PtrDict::write ( QDataStream & s, Q3PtrCollection::Item item ) const `[virtual protected]`

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

See also read().

### Q3PtrDict<type> & Q3PtrDict::operator= ( const Q3PtrDict<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 * Q3PtrDict::operator[] ( void * key ) const

Returns the item associated with key, or 0 if the key does not exist in the dictionary.

If there are two or more items with equal keys, then the most recently inserted item will be found.

Equivalent to the find() function.

See also find().