path: root/doc/qdict.doc

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/*****************************************************************************
  QDict documentation
 *****************************************************************************/

/*!
    \class QDict
    \brief The QDict class is a template class that provides a
    dictionary based on QString keys.

    \ingroup collection
    \ingroup tools
    \mainclass

    \important autoDelete setAutoDelete

    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 \c 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:
    \code
    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;
    \endcode
    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:
    \code
    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 );
    }
    \endcode
    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.

    \sa QDictIterator, QAsciiDict, QIntDict, QPtrDict
*/


/*!
    \fn QDict::QDict( int size, bool caseSensitive )

    Constructs a dictionary optimized for less than \a size entries.

    We recommend setting \a 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 \a caseSensitive is TRUE (the default), keys which differ only
    by case are considered different.
*/

/*!
    \fn QDict::QDict( const QDict<type> &dict )

    Constructs a copy of \a dict.

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

/*!
    \fn 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.

    \sa setAutoDelete()
*/

/*!
    \fn QDict<type> &QDict::operator=(const QDict<type> &dict)

    Assigns \a dict to this dictionary and returns a reference to this
    dictionary.

    This dictionary is first cleared, then each item in \a dict is
    inserted into this dictionary. Only the pointers are copied
    (shallow copy), unless newItem() has been reimplemented.
*/

/*!
    \fn uint QDict::count() const

    Returns the number of items in the dictionary.

    \sa isEmpty()
*/

/*!
    \fn uint QDict::size() const

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

    \sa count()
*/

/*!
    \fn void QDict::resize( uint newsize )

    Changes the size of the hash table to \a newsize. The contents of
    the dictionary are preserved, but all iterators on the dictionary
    become invalid.
*/

/*!
    \fn bool QDict::isEmpty() const

    Returns TRUE if the dictionary is empty, i.e. count() == 0;
    otherwise returns FALSE.

    \sa count()
*/

/*!
    \fn void QDict::insert( const QString &key, const type *item )

    Inserts the key \a key with value \a item into the dictionary.

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

    \a item may not be 0.

    \sa replace()
*/

/*!
    \fn void QDict::replace( const QString &key, const type *item )

    Replaces the value of the key, \a key with \a item.

    If the item does not already exist, it will be inserted.

    \a item may not be 0.

    Equivalent to:
    \code
	QDict<char> dict;
	    ...
	if ( dict.find( key ) )
	    dict.remove( key );
	dict.insert( key, item );
    \endcode

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

    \sa insert()
*/

/*!
    \fn bool QDict::remove( const QString &key )

    Removes the item with \a 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 \link
    QPtrCollection::setAutoDelete() auto-deletion\endlink 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.

    \sa take(), clear(), setAutoDelete()
*/

/*!
    \fn type *QDict::take( const QString &key )

    Takes the item with \a key out of the dictionary without deleting
    it (even if \link QPtrCollection::setAutoDelete()
    auto-deletion\endlink 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.

    \sa remove(), clear(), setAutoDelete()
*/

/*!
    \fn void QDict::clear()

    Removes all items from the dictionary.

    The removed items are deleted if \link
    QPtrCollection::setAutoDelete() auto-deletion\endlink is enabled.

    All dictionary iterators that operate on the dictionary are reset.

    \sa remove(), take(), setAutoDelete()
*/

/*!
    \fn type *QDict::find( const QString &key ) const

    Returns the item with key \a 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.

    \sa operator[]()
*/

/*!
    \fn type *QDict::operator[]( const QString &key ) const

    Returns the item with key \a 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.

    \sa find()
*/

/*!
    \fn void QDict::statistics() const

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

/*!
    \fn QDataStream& QDict::read( QDataStream &s, QPtrCollection::Item &item )

    Reads a dictionary item from the stream \a s and returns a
    reference to the stream.

    The default implementation sets \a item to 0.

    \sa write()
*/

/*!
    \fn QDataStream& QDict::write( QDataStream &s, QPtrCollection::Item ) const

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

    \sa read()
*/

/*****************************************************************************
  QDictIterator documentation
 *****************************************************************************/

/*!
    \class QDictIterator qdict.h
    \brief The QDictIterator class provides an iterator for QDict collections.

    \ingroup collection
    \ingroup tools

    QDictIterator is implemented as a template class. Define a
    template instance QDictIterator\<X\> to create a dictionary
    iterator that operates on QDict\<X\> (dictionary of X*).

    The traversal order is arbitrary; when we speak of the "first",
    "last" and "next" item we are talking in terms of this arbitrary
    order.

    Multiple iterators may independently traverse the same dictionary.
    A QDict knows about all the iterators that are operating on the
    dictionary. When an item is removed from the dictionary, QDict
    updates all iterators that are referring to the removed item to
    point to the next item in the (arbitrary) traversal order.

    Example:
    \code
    QDict<QLineEdit> fields;
    fields.insert( "forename", new QLineEdit( this ) );
    fields.insert( "surname", new QLineEdit( this ) );
    fields.insert( "age", new QLineEdit( this ) );

    fields["forename"]->setText( "Homer" );
    fields["surname"]->setText( "Simpson" );
    fields["age"]->setText( "45" );

    QDictIterator<QLineEdit> it( fields );
    for( ; it.current(); ++it )
	cout << it.currentKey() << ": " << it.current()->text() << endl;
    cout << endl;

    // Output (random order):
    //	age: 45
    //	surname: Simpson
    //	forename: Homer
    \endcode
    In the example we insert some pointers to line edits into a
    dictionary, then iterate over the dictionary printing the strings
    associated with the line edits.

    \sa QDict
*/

/*!
    \fn QDictIterator::QDictIterator( const QDict<type> &dict )

    Constructs an iterator for \a dict. The current iterator item is
    set to point to the first item in the dictionary, \a dict. First
    in this context means first in the arbitrary traversal order.
*/

/*!
    \fn QDictIterator::~QDictIterator()

    Destroys the iterator.
*/

/*!
    \fn uint QDictIterator::count() const

    Returns the number of items in the dictionary over which the
    iterator is operating.

    \sa isEmpty()
*/

/*!
    \fn bool QDictIterator::isEmpty() const

    Returns TRUE if the dictionary is empty, i.e. count() == 0;
    otherwise returns FALSE.

    \sa count()
*/

/*!
    \fn type *QDictIterator::toFirst()

    Resets the iterator, making the first item the first current item.
    First in this context means first in the arbitrary traversal
    order. Returns a pointer to this item.

    If the dictionary is empty it sets the current item to 0 and
    returns 0.
*/

/*!
  \fn type *QDictIterator::operator*()
  \internal
*/

/*!
    \fn QDictIterator::operator type*() const

    Cast operator. Returns a pointer to the current iterator item.
    Same as current().
*/


/*!
    \fn type *QDictIterator::current() const

    Returns a pointer to the current iterator item's value.
*/

/*!
    \fn QString QDictIterator::currentKey() const

    Returns the current iterator item's key.
*/

/*!
    \fn type *QDictIterator::operator()()

    Makes the next item current and returns the original current item.

    If the current iterator item was the last item in the dictionary
    or if it was 0, 0 is returned.
*/

/*!
    \fn type *QDictIterator::operator++()

    Prefix ++ makes the next item current and returns the new current
    item.

    If the current iterator item was the last item in the dictionary
    or if it was 0, 0 is returned.
*/

/*!
  \fn type *QDictIterator::operator+=( uint jump )
  \internal
  Sets the current item to the item \a jump positions after the current item,
  and returns a pointer to that item.

  If that item is beyond the last item or if the dictionary is empty,
  it sets the current item to 0 and returns 0.
*/