QDict Class Reference

The QDict class is a template class that provides a dictionary based on char* keys. More...

#include <qdict.h>

Inherits QGDict.

List of all member functions.

Public Members

• QDict (int size=17, bool caseSensitive=TRUE, bool copyKeys=TRUE)
• QDict (const QDict<type> &dict)
• ~QDict ()
• QDict<type>& operator= (const QDict<type> &dict)
• virtual uint count () const
• uint size () const
• bool isEmpty () const
• void insert (const char *key, const type *item)
• void replace (const char *key, const type *item)
• bool remove (const char *key)
• type* take (const char *key)
• virtual void clear ()
• type* find (const char *key) const
• type* operator[] (const char *key) const
• void statistics () const

Detailed Description

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

A dictionary is a collection that associates an item with a key. The key is used for inserting and looking up an item. QDict has char* keys.

The dictionary has very fast insertion and lookup.

Example:

    #include <qdict.h>
    #include <stdio.h>

    void main()
    {
        QDict<char> dict( 17, FALSE );  // case insensitive dict of char*

        dict.insert( "France", "Paris" );
        dict.insert( "Russia", "Moscow" );
        dict.insert( "Norway", "Oslo" );

        printf( "%s\n", dict["Norway"] );
        printf( "%s\n", dict["FRANCE"] );
        printf( "%s\n", dict["russia"] );

        if ( !dict["Italy"] )
            printf( "Italy not defined\n" );
    }

Program output:

        Oslo
        Paris
        Moscow
        Italy not defined

The dictionary in our example maps char* keys to char* items. Note that the mapping is case insensitive (set in the constructor). QDict implements the [] operator to lookup an item.

A QDict can also be instantiated through a macro expansion, but this is necessary only for compilers that do not support templates. See the collection classes documentation for a general discussion on template-based versus macro-based collections.

QDict is implemented by QGDict 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. 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 QDict 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.

The size of the hash array 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.

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.

Example:

    #include <qdict.h>
    #include <stdio.h>

    void main()
    {
        QDict<char> dict;               // case sensitive dict of char*

        dict.insert( "Germany", "Berlin" );
        dict.insert( "Germany", "Bonn" );

        printf( "%s\n", dict["Germany"] );
        dict.remove( "Germany" );       // Oct 3rd 1990
        printf( "%s\n", dict["Germany"] );
    }

Program output:

        Bonn
        Berlin

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

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

When inserting an item into a dictionary, only the pointer is copied, not the item itself. This is called a shallow copy. It is possible to make the dictionary copy all of the item's data (known as a deep copy) when an item is inserted. insert() calls the virtual function QCollection::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 QCollection::deleteItem() is called. QDict's default implementation is to delete the item if auto-deletion is enabled.

See also: QDictIterator, QIntDict and Collection Classes

Member Function Documentation

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

Constructs copy of dict.

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

QDict::QDict ( int size=17, bool caseSensitive=TRUE, bool copyKeys=TRUE)

Constructs a dictionary with the following properties:

Arguments:

• size is the size of the internal hash array.
• caseSensitive specifies whether to use case sensitive lookup or not.
• copyKeys specifies whether to copy the key strings.