QDict(3qt)QDict(3qt)NAMEQDict - Template class that provides a dictionary based on QString keys
SYNOPSIS
#include <qdict.h>
Inherits QPtrCollection.
Public Members
QDict ( int size = 17, bool caseSensitive = 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 QString & key, const type * item )
void replace ( const QString & key, const type * item )
bool remove ( const QString & key )
type * take ( const QString & key )
type * find ( const QString & key ) const
type * operator[] ( const QString & 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
DESCRIPTION
The QDict class is a template class that provides a dictionary based on
QString keys.
QMap is an STL-compatible alternative to this class.
QDict is implemented as a template class. Define a template instance
QDict<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 QString
used for insertion, removal and lookup. The value is a pointer.
Dictionaries provide very fast insertion and lookup.
If you want to use non-Unicode, plain 8-bit char* keys, use the
QAsciiDict template. A QDict has the same performance as a QAsciiDict.
If you want to have a dictionary that maps QStrings to QStrings use
QMap.
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(); 0 pointers cannot be inserted. Items
are 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.
When an item is inserted, the key is converted (hashed) to an integer
index into an internal hash array. This makes lookup very fast.
Items with equal keys are allowed. When inserting two items with the
same key, only the last inserted item will be accessible (last in,
first out) until it is removed.
The QDictIterator 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 newItem() if you want deep copies.
When removing a dictionary item, the virtual function
QPtrCollection::deleteItem() is called. QDict's default implementation
is to delete the item if auto-deletion is enabled.
Example #1:
QDict<QLineEdit> fields; // QString keys, QLineEdit* values
fields.insert( "forename", new QLineEdit( this ) );
fields.insert( "surname", new QLineEdit( this ) );
fields["forename"]->setText( "Homer" );
fields["surname"]->setText( "Simpson" );
QDictIterator<QLineEdit> it( fields ); // See QDictIterator
for( ; it.current(); ++it )
cout << it.currentKey() << ": " << it.current()->text() << endl;
cout << endl;
if ( fields["forename"] && fields["surname"] )
cout << fields["forename"]->text() << " "
<< fields["surname"]->text() << endl; // Prints "Homer Simpson"
fields.remove( "forename" ); // Does not delete the line edit
if ( ! fields["forename"] )
cout << "forename is not in the dictionary" << endl;
In this example we use a dictionary to keep track of the line edits
we're using. We insert each line edit into the dictionary with a unique
name and then access the line edits via the dictionary.
Example #2:
QStringList styleList = QStyleFactory::styles();
styleList.sort();
QDict<int> letterDict( 17, FALSE );
for ( QStringList::Iterator it = styleList.begin(); it != styleList.end(); ++it ) {
QString styleName = *it;
QString styleAccel = styleName;
if ( letterDict[styleAccel.left(1)] ) {
for ( uint i = 0; i < styleAccel.length(); i++ ) {
if ( ! letterDict[styleAccel.mid( i, 1 )] ) {
styleAccel = styleAccel.insert( i, '&' );
letterDict.insert(styleAccel.mid( i, 1 ), (const int *)1);
break;
}
}
} else {
styleAccel = "&" + styleAccel;
letterDict.insert(styleAccel.left(1), (const int *)1);
}
(void) new QAction( styleName, QIconSet(), styleAccel, parent );
}
In the example we are using the dictionary to provide fast random
access to the keys, and we don't care what the values are. The example
is used to generate a menu of QStyles, each with a unique accelerator
key (or no accelerator if there are no unused letters left).
We first obtain the list of available styles, then sort them so that
the menu items will be ordered alphabetically. Next we create a
dictionary of int pointers. The keys in the dictionary are each one
character long, representing letters that have been used for
accelerators. We iterate through our list of style names. If the first
letter of the style name is in the dictionary, i.e. has been used, we
iterate over all the characters in the style name to see if we can find
a letter that hasn't been used. If we find an unused letter we put the
accelerator ampersand (&) in front of it and add that letter to the
dictionary. If we can't find an unused letter the style will simply
have no accelerator. If the first letter of the style name is not in
the dictionary we use it for the accelerator and add it to the
dictionary. Finally we create a QAction for each style.
See also QDictIterator, QAsciiDict, QIntDict, QPtrDict, Collection
Classes, and Non-GUI Classes.
MEMBER FUNCTION DOCUMENTATIONQDict::QDict ( int size = 17, bool caseSensitive = TRUE )
Constructs a dictionary optimized for less than size entries.
We recommend setting size to a suitably large prime number (e.g. a
prime that's slightly larger than the expected number of entries). This
makes the hash distribution better which will lead to faster lookup.
If caseSensitive is TRUE (the default), keys which differ only by case
are considered different.
QDict::QDict ( const QDict<;type> & dict )
Constructs a copy of dict.
Each item in dict is inserted into this dictionary. Only the pointers
are copied (shallow copy).
QDict::~QDict ()
Removes all items from the dictionary and destroys it. If
setAutoDelete() is TRUE, each value is deleted. 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 QDict::clear () [virtual]
Removes all items from the dictionary.
The removed items are deleted if auto-deletion is enabled.
All dictionary iterators that operate on the dictionary are reset.
See also remove(), take(), and setAutoDelete().
Reimplemented from QPtrCollection.
uint QDict::count () const [virtual]
Returns the number of items in the dictionary.
See also isEmpty().
Reimplemented from QPtrCollection.
type * QDict::find ( const QString & key ) const
Returns the item with key 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 [] operator.
See also operator[]().
void QDict::insert ( const QString & key, const type * item )
Inserts the key key with value 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().
Example: themes/themes.cpp.
bool QDict::isEmpty () const
Returns TRUE if the dictionary is empty, i.e. count() == 0; otherwise
returns FALSE.
See also count().
QDict<;type> & QDict::operator= ( const QDict<type> & dict )
Assigns dict to this dictionary and returns a reference to this
dictionary.
This dictionary is first cleared, then each item in dict is inserted
into this dictionary. Only the pointers are copied (shallow copy),
unless newItem() has been reimplemented.
type * QDict::operator[] ( const QString & key ) const
Returns the item with key 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().
QDataStream & QDict::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 QDict::remove ( const QString & key )
Removes the item with key from the dictionary. Returns TRUE if
successful, i.e. if the item is in the dictionary; otherwise returns
FALSE.
If there are two or more items with equal keys, then the last item that
was inserted 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 traversal order.
See also take(), clear(), and setAutoDelete().
void QDict::replace ( const QString & key, const type * item )
Replaces the value of the key, key with item.
If the item does not already exist, it will be inserted.
item may not be 0.
Equivalent to:
QDict<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 item that
was inserted will be replaced.
See also insert().
void QDict::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.
See also autoDelete().
Examples:
uint QDict::size () const
Returns the size of the internal hash array (as specified in the
constructor).
See also count().
void QDict::statistics () const
Debugging-only function that prints out the dictionary distribution
using qDebug().
type * QDict::take ( const QString & key )
Takes the item 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 will be taken.
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 & QDict::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().
SEE ALSO
http://doc.trolltech.com/qdict.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports help us to
help you. Thank you.
The definitive Qt documentation is provided in HTML format; it is
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If you find errors in this manual page, please report them to qt-
bugs@trolltech.com. Please include the name of the manual page
(qdict.3qt) and the Qt version (3.3.8).
Trolltech AS 2 February 2007 QDict(3qt)
