path: root/doc/qmap.doc

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/*****************************************************************************
  QMap documentation
 *****************************************************************************/

/*!
    \class QMap qmap.h
    \brief The QMap class is a value-based template class that
    provides a dictionary.

    \ingroup qtl
    \ingroup tools
    \ingroup shared
    \mainclass

    QMap is a Qt implementation of an STL-like map container. It can
    be used in your application if the standard \c map is not
    available on all your target platforms. QMap is part of the \link
    qtl.html Qt Template Library\endlink.

    QMap\<Key, Data\> defines a template instance to create a
    dictionary with keys of type Key and values of type Data. QMap
    does not store pointers to the members of the map; instead, it
    holds a copy of every member. For this reason, QMap is
    value-based, whereas QPtrList and QDict are pointer-based.

    QMap contains and manages a collection of objects of type Data
    with associated key values of type Key and provides iterators that
    allow the contained objects to be addressed. QMap owns the
    contained items.

    Some classes cannot be used within a QMap. For example everything
    derived from QObject and thus all classes that implement widgets.
    Only values can be used in a QMap. To qualify as a value, the
    class must provide

    \list
    \i A copy constructor
    \i An assignment operator
    \i A default constructor, i.e. a constructor that does not take
    any arguments.
    \endlist

    Note that C++ defaults to field-by-field assignment operators and
    copy constructors if no explicit version is supplied. In many
    cases, this is sufficient.

    The class used for the key requires that the \c operator< is
    implemented to define ordering of the keys.

    QMap's function naming is consistent with the other Qt classes
    (e.g., count(), isEmpty()). QMap also provides extra functions for
    compatibility with STL algorithms, such as size() and empty().
    Programmers already familiar with the STL \c map can use these
    the STL-like functions if preferred.

    Example:
    \target qmap-eg
    \code
    #include <qstring.h>
    #include <qmap.h>
    #include <qstring.h>

    class Employee
    {
    public:
	Employee(): sn(0) {}
	Employee( const QString& forename, const QString& surname, int salary )
	    : fn(forename), sn(surname), sal(salary)
	{ }

	QString forename() const { return fn; }
	QString surname() const { return sn; }
	int salary() const { return sal; }
	void setSalary( int salary ) { sal = salary; }

    private:
	QString fn;
	QString sn;
	int sal;
    };

    int main(int argc, char **argv)
    {
	QApplication app( argc, argv );

	typedef QMap<QString, Employee> EmployeeMap;
	EmployeeMap map;

	map["JD001"] = Employee("John", "Doe", 50000);
	map["JW002"] = Employee("Jane", "Williams", 80000);
	map["TJ001"] = Employee("Tom", "Jones", 60000);

	Employee sasha( "Sasha", "Hind", 50000 );
	map["SH001"] = sasha;
	sasha.setSalary( 40000 );

	EmployeeMap::Iterator it;
	for ( it = map.begin(); it != map.end(); ++it ) {
	    printf( "%s: %s, %s earns %d\n",
		    it.key().latin1(),
		    it.data().surname().latin1(),
		    it.data().forename().latin1(),
		    it.data().salary() );
	}
	return 0;
    }
    \endcode

    Program output:
    \code
    JD001: Doe, John earns 50000
    JW002: Williams, Jane earns 80000
    SH001: Hind, Sasha earns 50000
    TJ001: Jones, Tom earns 60000
    \endcode

    The latest changes to Sasha's salary did not affect the value in
    the list because the map created a copy of Sasha's entry. In
    addition, notice that the items are sorted alphabetically (by key)
    when iterating over the map.

    There are several ways to find items in a map. The begin() and
    end() functions return iterators to the beginning and end of the
    map. The advantage of using an iterator is that you can move
    forward or backward by incrementing/decrementing the iterator.
    The iterator returned by end() points to the element which is one
    past the last element in the container. The past-the-end iterator
    is still associated with the map it belongs to, however it is \e
    not dereferenceable; operator*() will not return a well-defined
    value. If the map is empty, the iterator returned by begin() will
    equal the iterator returned by end().

    Another way to find an element in the map is by using the find()
    function. This returns an iterator pointing to the desired item or
    to the end() iterator if no such element exists.

    Another approach uses the operator[]. But be warned: if the map
    does not contain an entry for the element you are looking for,
    operator[] inserts a default value. If you do not know that the
    element you are searching for is really in the list, you should
    not use operator[]. The following example illustrates this:

    \code
	QMap<QString,QString> map;
	map["Clinton"] = "Bill";
	str << map["Clinton"] << map["Bush"] << endl;
    \endcode

    The code fragment will print out "Clinton", "". Since the value
    associated with the "Bush" key did not exist, the map inserted a
    default value (in this case, an empty string). If you are not
    sure whether a certain element is in the map, you should use
    find() and iterators instead.

    If you just want to know whether a certain key is contained in the
    map, use the contains() function. In addition, count() tells you
    how many keys are in the map.

    It is safe to have multiple iterators at the same time. If some
    member of the map is removed, only iterators pointing to the
    removed member become invalid; inserting in the map does not
    invalidate any iterators.

    Since QMap is value-based, there is no need to be concerned about
    deleting items in the map. The map holds its own copies and will
    free them if the corresponding member or the map itself is
    deleted.

    QMap is implicitly shared. This means you can just make copies of
    the map in time O(1). If multiple QMap instances share the same
    data and one is modifying the map's data, this modifying instance
    makes a copy and modifies its private copy: so it does not affect
    other instances. If a QMap is being used in a multi-threaded
    program, you must protect all access to the map. See \l QMutex.

    There are a couple of ways of inserting new items into the map.
    One uses the insert() method; the other uses operator[]:
    \code
    QMap<QString, QString> map;
    map["Clinton"] = "Bill";
    map.insert( "Bush", "George" );
    \endcode

    Items can also be removed from the map in several ways. One way is
    to pass an iterator to remove(). Another way is to pass a key
    value to remove(), which will delete the entry with the requested
    key. In addition you can clear the entire map using the clear()
    method.

    \sa QMapIterator
*/


/*! \enum  QMap::key_type
	The map's key type. */
/*! \enum  QMap::mapped_type
	The map's data type. */
/*! \enum  QMap::value_type
	Corresponds to QPair\<key_type, mapped_type\>. */
/*! \enum  QMap::ValueType
	Corresponds to QPair\<key_type, mapped_type\>, Qt style.*/
/*! \enum  QMap::pointer
	Pointer to value_type.*/
/*! \enum  QMap::const_pointer
	Const pointer to value_type.*/
/*! \enum  QMap::reference
	Reference to value_type.*/
/*! \enum  QMap::const_reference
	Const reference to value_type.*/
/*! \enum  QMap::size_type
	An unsigned integral type, used to represent various sizes. */
/*! \enum  QMap::iterator
	The map's iterator type.*/
/*! \enum QMap::Iterator
	The map's iterator type, Qt style. */
/*! \enum  QMap::const_iterator
	The map's const iterator type.*/
/*! \enum  QMap::ConstIterator
	The map's const iterator type, Qt style.*/
/*! \enum QMap::difference_type
    \internal */
/*! \enum QMap::Priv
    \internal */

/*!
    \fn QMap::QMap()

    Constructs an empty map.
*/

/*!
    \fn QMap::QMap( const QMap<Key,T>& m )

    Constructs a copy of \a m.

    This operation costs O(1) time because QMap is implicitly shared.
    This makes returning a QMap from a function very fast. If a shared
    instance is modified, it will be copied (copy-on-write), and this
    takes O(n) time.
*/

/*!
    \fn QMap::QMap( const std::map<Key,T>& m )

    Constructs a copy of \a m.
*/

/*!
    \fn QMap<Key,T>& QMap::operator= ( const std::map<Key,T>& m )

    \overload

    Assigns \a m to this map and returns a reference to this map.

    All iterators of the current map become invalidated by this
    operation.
*/

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

    Destroys the map. References to the values in the map and all
    iterators of this map become invalidated. Since QMap is highly
    tuned for performance you won't see warnings if you use invalid
    iterators, because it is not possible for an iterator to check
    whether it is valid or not.
*/

/*!
    \fn QMap<Key, T>& QMap::operator= (const QMap<Key, T>& m)

    Assigns \a m to this map and returns a reference to this map.

    All iterators of the current map become invalidated by this
    operation. The cost of such an assignment is O(1), because QMap is
    implicitly shared.
*/

/*!
    \fn T& QMap::operator[] ( const Key& k )

    Returns the value associated with the key \a k. If no such key is
    present, an empty item is inserted with this key and a reference
    to the empty item is returned.

    You can use this operator both for reading and writing:
    \code
    QMap<QString, QString> map;
    map["Clinton"] = "Bill";
    stream << map["Clinton"];
    \endcode
*/

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

    Removes all items from the map.

    \sa remove()
*/

/*!
    \fn Iterator QMap::find( const Key& k )

    Returns an iterator pointing to the element with key \a k in the
    map.

    Returns end() if no key matched.

    \sa QMapIterator
*/

/*!
    \fn ConstIterator QMap::find( const Key& k ) const

    \overload

    Returns an iterator pointing to the element with key \a k in the
    map.

    Returns end() if no key matched.

    \sa QMapConstIterator
*/

/*!
    \fn Iterator QMap::begin()

    Returns an iterator pointing to the first element in the map. This
    iterator equals end() if the map is empty.

    The items in the map are traversed in the order defined by
    operator\<(Key, Key).

    \sa end() QMapIterator
*/

/*!
    \fn ConstIterator QMap::begin() const

    \overload

    \sa end() QMapConstIterator
*/

/*!
    \fn ConstIterator QMap::constBegin() const

    Returns an iterator pointing to the first element in the map. This
    iterator equals end() if the map is empty.

    The items in the map are traversed in the order defined by
    operator\<(Key, Key).

    \sa constEnd() QMapConstIterator
*/

/*!
    \fn Iterator QMap::end()

    The iterator returned by end() points to the element which is one
    past the last element in the container. The past-the-end iterator
    is still associated with the map it belongs to, but it is \e not
    dereferenceable; operator*() will not return a well-defined value.

    This iterator equals begin() if the map is empty.

    \sa begin() QMapIterator
*/

/*!
    \fn ConstIterator QMap::end() const

    \overload
*/

/*!
    \fn ConstIterator QMap::constEnd() const

    The iterator returned by end() points to the element which is one
    past the last element in the container. The past-the-end iterator
    is still associated with the map it belongs to, but it is \e not
    dereferenceable; operator*() will not return a well-defined value.

    This iterator equals constBegin() if the map is empty.

    \sa constBegin() QMapConstIterator
*/

/*!
    \fn void QMap::detach()

    If the map does not share its data with another QMap instance,
    nothing happens; otherwise the function creates a new copy of this
    map and detaches from the shared one. This function is called
    whenever the map is modified. The implicit sharing mechanism is
    implemented this way.
*/


/*!
    \fn QDataStream& operator>>( QDataStream& s, QMap<Key,T>& m )

    \relates QMap

    Reads the map \a m from the stream \a s. The types \e Key and \e T
    must implement the streaming operator as well.
*/

/*!
    \fn QDataStream& operator<<( QDataStream& s, const QMap<Key,T>& m )

    \relates QMap

    Writes the map \a m to the stream \a s. The types \e Key and \e T
    must implement the streaming operator as well.
*/

/*!
    \fn size_type QMap::size() const

    Returns the number of items in the map.

    This function is provided for STL compatibility. It is equivalent
    to count().

    \sa empty()
*/

/*!
    \fn bool QMap::empty() const

    Returns TRUE if the map contains no items; otherwise returns
    FALSE.

    This function is provided for STL compatibility. It is equivalent
    to isEmpty().

    \sa size()
*/

/*!
    \fn QPair<iterator,bool> QMap::insert( const value_type& x )

    \overload

    Inserts the (key, value) pair \a x into the map. \a x is a QPair
    whose \c first element is a key to be inserted and whose \c second
    element is the associated value to be inserted. Returns a pair
    whose \c first element is an iterator pointing to the inserted
    item and whose \c second element is a bool indicating TRUE if \a x
    was inserted and FALSE if it was not inserted, e.g. because it was
    already present.

    \sa replace()
*/

/*!
    \fn void QMap::erase( iterator it )

    Removes the item associated with the iterator \a it from the map.

    This function is provided for STL compatibility. It is equivalent
    to remove().

    \sa clear()
*/

/*!
    \fn void QMap::erase( const key_type& k )

    \overload

    Removes the item with the key \a k from the map.
*/

/*!
    \fn size_type QMap::count( const key_type& k ) const

    Returns the number of items whose key is \a k. Since QMap does not
    allow duplicate keys, the return value is always 0 or 1.

    This function is provided for STL compatibility.
*/

/*!
    \fn Iterator QMap::replace( const Key& k, const T& v )

    Replaces the value of the element with key \a k, with the value \a
    v.

    \sa insert() remove()
*/

/*!
    \fn const T& QMap::operator[] ( const Key& k ) const

    \overload

    \warning This function differs from the non-const version of the
    same function. It will \e not insert an empty value if the key \a
    k does not exist. This may lead to logic errors in your program.
    You should check if the element exists before calling this
    function.

    Returns the value associated with the key \a k. If no such key is
    present, a reference to an empty item is returned.
*/

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

    \overload

    Returns the number of items in the map.

    \sa isEmpty()
*/

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

    Returns TRUE if the map contains no items; otherwise returns
    FALSE.

    \sa count()
*/

/*!
    \fn Iterator QMap::insert( const Key& key, const T& value, bool overwrite )

    Inserts a new item with the key, \a key, and a value of \a value.
    If there is already an item whose key is \a key, that item's value
    is replaced with \a value, unless \a overwrite is FALSE (it is
    TRUE by default). In this case an iterator to this item is
    returned, else an iterator to the new item is returned.

*/

/*!
    \fn void QMap::remove( iterator it )

    Removes the item associated with the iterator \a it from the map.

    \sa clear()
*/

/*!
    \fn void QMap::remove( const Key& k )

    \overload

    Removes the item with the key \a k from the map.
*/

/*!
    \fn bool QMap::contains( const Key& k ) const

    Returns TRUE if the map contains an item with key \a k; otherwise
    returns FALSE.
*/


/*****************************************************************************
  QMapIterator documentation
 *****************************************************************************/

/*!
    \class QMapIterator qmap.h
    \brief The QMapIterator class provides an iterator for QMap.

    \ingroup qtl
    \ingroup tools

    You cannot create an iterator by yourself. Instead, you must ask a
    map to give you one. An iterator is as big as a pointer; on 32-bit
    machines that means 4 bytes, on 64-bit machines, 8 bytes. That
    makes copying iterators very fast. Iterators behave in a similar
    way to pointers, and they are almost as fast as pointers. See the
    \link qmap.html#qmap-eg QMap example\endlink.

    QMap is highly optimized for performance and memory usage, but the
    trade-off is that you must be more careful. The only way to
    traverse a map is to use iterators. QMap does not know about its
    iterators, and the iterators don't even know to which map they
    belong. That makes things fast but a bit dangerous because it is
    up to you to make sure that the iterators you are using are still
    valid. QDictIterator will be able to give warnings, whereas
    QMapIterator may end up in an undefined state.

    For every Iterator there is also a ConstIterator. You must use the
    ConstIterator to access a QMap in a const environment or if the
    reference or pointer to the map is itself const. Its semantics are
    the same, but it only returns const references to the item it
    points to.

    \sa QMap QMapConstIterator
*/

/*! \enum  QMapIterator::iterator_category
	The type of iterator category, \c std::bidirectional_iterator_tag. */
/*! \enum  QMapIterator::value_type
	The type of value. */
/*! \enum  QMapIterator::pointer
	Pointer to value_type. */
/*! \enum  QMapIterator::reference
	Reference to value_type. */
/*! \enum QMapIterator::difference_type
    \internal */
/*! \enum QMapIterator::NodePtr
    \internal */

/*!
    \fn QMapIterator::QMapIterator()

    Creates an uninitialized iterator.
*/

/*!
    \fn QMapIterator::QMapIterator (QMapNode<K, T> * p)

    Constructs an iterator starting at node \a p.
*/

/*!
    \fn QMapIterator::QMapIterator( const QMapIterator<K,T>& it )

    Constructs a copy of the iterator, \a it.
*/

/*!
    \fn QMapIterator<K,T>& QMapIterator::operator++()

    Prefix ++ makes the succeeding item current and returns an
    iterator pointing to the new current item. The iterator cannot
    check whether it reached the end of the map. Incrementing the
    iterator returned by end() causes undefined results.
*/

/*!
    \fn QMapIterator<K,T> QMapIterator::operator++(int)

    \overload

    Postfix ++ makes the succeeding item current and returns an
    iterator pointing to the new current item. The iterator cannot
    check whether it reached the end of the map. Incrementing the
    iterator returned by end() causes undefined results.
*/

/*!
    \fn QMapIterator<K,T>& QMapIterator::operator--()

    Prefix -- makes the previous item current and returns an iterator
    pointing to the new current item. The iterator cannot check
    whether it reached the beginning of the map. Decrementing the
    iterator returned by begin() causes undefined results.
*/

/*!
    \fn QMapIterator<K,T> QMapIterator::operator--(int)

    \overload

    Postfix -- makes the previous item current and returns an iterator
    pointing to the new current item. The iterator cannot check
    whether it reached the beginning of the map. Decrementing the
    iterator returned by begin() causes undefined results.
*/

/*!
    \fn T& QMapIterator::operator*()

    Dereference operator. Returns a reference to the current item's
    data. The same as data().
*/

/*!
    \fn const T& QMapIterator::operator*() const

    \overload

    Dereference operator. Returns a const reference to the current
    item's data. The same as data().
*/

/*!
    \fn bool QMapIterator::operator==( const QMapIterator<K,T>& it ) const

    Compares the iterator to the \a it iterator and returns TRUE if
    they point to the same item; otherwise returns FALSE.
*/

/*!
    \fn bool QMapIterator::operator!=( const QMapIterator<K,T>& it ) const

    Compares the iterator to the \a it iterator and returns FALSE if
    they point to the same item; otherwise returns TRUE.
*/

/*!
    \fn T& QMapIterator::data()

    Returns a reference to the current item's data.
*/

/*!
    \fn const T& QMapIterator::data() const

    \overload

    Returns a const reference to the current item's data.
*/

/*!
    \fn const K& QMapIterator::key() const

    Returns a const reference to the current item's key.
*/

/*!
    \fn QValueList<Key> QMap::keys() const

    Returns a list of all the keys in the map, in order.
*/

/*!
    \fn QValueList<T> QMap::values() const

    Returns a list of all the values in the map, in key order.
*/

/*****************************************************************************
  QMapConstIterator documentation
 *****************************************************************************/

/*!
    \class QMapConstIterator qmap.h
    \brief The QMapConstIterator class provides an iterator for QMap.

    \ingroup qtl
    \ingroup tools

    In contrast to QMapIterator, this class is used to iterate over a
    const map. It does not allow you to modify the values of the map
    because this would break the const semantics.

    For more information on QMap iterators, see \l{QMapIterator} and
    the \link qmap.html#qmap-eg QMap example\endlink.

    \sa QMap QMapIterator
*/

/*! \enum  QMapConstIterator::iterator_category
	The type of iterator category, \c std::bidirectional_iterator_tag. */
/*! \enum  QMapConstIterator::value_type
	The type of const value. */
/*! \enum  QMapConstIterator::pointer
	Const pointer to value_type. */
/*! \enum  QMapConstIterator::reference
	Const reference to value_type. */
/*! \enum QMapConstIterator::difference_type
    \internal */
/*! \enum QMapConstIterator::NodePtr
    \internal */


/*!
    \fn QMapConstIterator::QMapConstIterator()

    Constructs an uninitialized iterator.
*/

/*!
    \fn QMapConstIterator::QMapConstIterator (QMapNode<K, T> * p)

    Constructs an iterator starting at node \a p.
*/

/*!
    \fn QMapConstIterator::QMapConstIterator( const QMapConstIterator<K,T>& it )

    Constructs a copy of the iterator, \a it.
*/

/*!
    \fn QMapConstIterator::QMapConstIterator( const QMapIterator<K,T>& it )

    Constructs a copy of the iterator, \a it.
*/

/*!
    \fn QMapConstIterator<K,T>& QMapConstIterator::operator++()

    Prefix ++ makes the succeeding item current and returns an
    iterator pointing to the new current item. The iterator cannot
    check whether it reached the end of the map. Incrementing the
    iterator returned by end() causes undefined results.
*/

/*!
    \fn QMapConstIterator<K,T> QMapConstIterator::operator++(int)

    \overload

    Postfix ++ makes the succeeding item current and returns an
    iterator pointing to the new current item. The iterator cannot
    check whether it reached the end of the map. Incrementing the
    iterator returned by end() causes undefined results.
*/

/*!
    \fn QMapConstIterator<K,T>& QMapConstIterator::operator--()

    Prefix -- makes the previous item current and returns an iterator
    pointing to the new current item. The iterator cannot check
    whether it reached the beginning of the map. Decrementing the
    iterator returned by begin() causes undefined results.
*/

/*!
    \fn QMapConstIterator<K,T> QMapConstIterator::operator--(int)

    \overload

    Postfix -- makes the previous item current and returns an iterator
    pointing to the new current item. The iterator cannot check
    whether it reached the beginning of the map. Decrementing the
    iterator returned by begin() causes undefined results.
*/

/*!
    \fn const T& QMapConstIterator::operator*() const

    Dereference operator. Returns a const reference to the current
    item's data. The same as data().
*/

/*!
    \fn bool QMapConstIterator::operator==( const QMapConstIterator<K,T>& it ) const

    Compares the iterator to the \a it iterator and returns TRUE if
    they point to the same item; otherwise returns FALSE.
*/

/*!
    \fn bool QMapConstIterator::operator!=( const QMapConstIterator<K,T>& it ) const

    Compares the iterator to the \a it iterator and returns FALSE if
    they point to the same item; otherwise returns TRUE.
*/

/*!
    \fn const T& QMapConstIterator::data() const

    Returns a const reference to the current item's data.
*/

/*!
    \fn const K& QMapConstIterator::key() const

    Returns a const reference to the current item's key.
*/