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QIntDict Class Reference

The QIntDict class is a template class that provides a dictionary based on long keys. More...

#include <qintdict.h>

Inherits QPtrCollection.

List of all member functions.

Public Members

Important Inherited Members

Protected Members


Detailed Description

The QIntDict class is a template class that provides a dictionary based on long keys.

QIntDict is implemented as a template class. Define a template instance QIntDict<X> to create a dictionary that operates on pointers to X, or X*.

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

The size() of the dictionary is very important. In order to get good performance, you should use a suitably large prime number. Suitable means equal to or larger than the maximum expected number of dictionary items. Size is set in the constructor but may be changed with resize().

Items are inserted with insert(), and removed with remove(). All the items in a dictionary can be removed with clear(). The number of items in the dictionary is returned by count(). If the dictionary contains no items isEmpty() returns TRUE. You can change an item's value with replace(). Items are looked up with operator[](), or with find() which return a pointer to the value or 0 if the given key does not exist. You can take an item out of the dictionary with take().

Calling setAutoDelete(TRUE) for a dictionary tells it to delete items that are removed. The default behaviour is not to delete items when they are removed.

QIntDict is implemented as a hash array with a fixed number of entries. Each array entry points to a singly linked list of buckets, in which the dictionary items are stored. When an item is inserted with a key, the key is converted (hashed) to an integer index into the hash array using the mod function. The item is inserted before the first bucket in the list of buckets.

Looking up an item is normally very fast. The key is again hashed to an array index. Then QIntDict scans the list of buckets and returns the item found or null if the item was not found. You cannot insert null pointers into a dictionary.

Items with equal keys are allowed. When inserting two items with the same key, only the last inserted item will be visible (last in, first out) until it is removed.

The QIntDictIterator class can traverse the dictionary, but only in an arbitrary order. Multiple iterators may independently traverse the same dictionary.

When inserting an item into a dictionary, only the pointer is copied, not the item itself, i.e. a shallow copy is made. It is possible to make the dictionary copy all of the item's data (a deep copy) when an item is inserted. insert() calls the virtual function QPtrCollection::newItem() for the item to be inserted. Inherit a dictionary and reimplement it if you want deep copies.

When removing a dictionary item, the virtual function QPtrCollection::deleteItem() is called. QIntDict's default implementation is to delete the item if auto-deletion is enabled.

Example:

    #include <qintdict.h>
    #include <stdio.h>

    int main()
    {
        QIntDict<char> dict; // maps long ==> char*

        dict.insert( 33, "France" );
        dict.insert(  7, "Russia" );
        dict.insert( 49, "Norway" );
        dict.insert( 28, "Belgium" );

        printf( "%s\n", dict[49] );
        printf( "%s\n", dict[33] );
        printf( "%s\n", dict[7] );
        printf( "%s\n", dict[28] );

        dict.remove( 28 );

        if ( !dict[39] ) 
            printf( "39 not defined\n" ); // Never existed
        if ( !dict[28] ) 
            printf( "28 not defined\n" ); // Removed

        return 0;
    }
  

Program output:

    Norway
    France
    Russia
    Belgium
    39 not defined
    28 not defined
  

The dictionary in our example maps long keys to char* items. QIntDict implements the [] operator to look up an item.

See also QIntDictIterator, QDict, QAsciiDict, QPtrDict and Collection Classes.


Member Function Documentation

QIntDict::QIntDict ( int size = 17 )

Constructs a dictionary using an internal hash array of 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 loopup faster.

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

Constructs a copy of dict.

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

QIntDict::~QIntDict ()

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 QIntDict::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 QIntDict::count () const [virtual]

Returns the number of items in the dictionary.

See also isEmpty().

Reimplemented from QPtrCollection.

type * QIntDict::find ( long 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 inserted of these will be found.

Equivalent to the [] operator.

See also operator[]().

Example: table/bigtable/main.cpp.

void QIntDict::insert ( long key, const type * item )

Insert item item into the dictionary using key key.

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

Null items are not allowed.

See also replace().

Example: scribble/scribble.cpp.

bool QIntDict::isEmpty () const

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

See also count().

QIntDict<type> & QIntDict::operator= ( const QIntDict<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 this dictionary. Only the pointers are copied (shallow copy), unless newItem() has been reimplemented.

type * QIntDict::operator[] ( long 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 inserted of these will be found.

Equivalent to the find() function.

See also find().

QDataStream & QIntDict::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 QIntDict::remove ( long key )

Removes the item associated with key from the dictionary. Returns TRUE if successful; otherwise returns FALSE, e.g. if the key does not exist in the dictionary.

If there are two or more items with equal keys, then the last inserted of these 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's traversing order.

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

Example: table/bigtable/main.cpp.

void QIntDict::replace ( long 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:

    QIntDict<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().

Example: table/bigtable/main.cpp.

void QIntDict::resize ( uint newsize )

Changes the size of the hashtable 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 can be quite 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.

See also autoDelete().

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

uint QIntDict::size () const

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

See also count().

void QIntDict::statistics () const

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

type * QIntDict::take ( long 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 inserted of these will be taken.

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's traversing order.

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

QDataStream & QIntDict::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().


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