Viadeo Twitter Google Bookmarks ! Facebook Digg del.icio.us MySpace Yahoo MyWeb Blinklist Netvouz Reddit Simpy StumbleUpon Bookmarks Windows Live Favorites 
Logo Documentation Qt ·  Page d'accueil  ·  Toutes les classes  ·  Toutes les fonctions  ·  Vues d'ensemble  · 

const_iterator Class Reference
(QMap::const_iterator)
[QtCore module]

The QMap::const_iterator class provides an STL-style const iterator for QMap and QMultiMap. More...

 #include <QMap>

Public Types

typedef iterator_category

Public Functions

const_iterator ()
const_iterator ( const iterator & other )
const Key & key () const
const T & value () const
bool operator!= ( const const_iterator & other ) const
const T & operator* () const
const_iterator operator+ ( int j ) const
const_iterator & operator++ ()
const_iterator operator++ ( int )
const_iterator & operator+= ( int j )
const_iterator operator- ( int j ) const
const_iterator & operator-- ()
const_iterator operator-- ( int )
const_iterator & operator-= ( int j )
const T * operator-> () const
bool operator== ( const const_iterator & other ) const

Detailed Description

The QMap::const_iterator class provides an STL-style const iterator for QMap and QMultiMap.

QMap features both STL-style iterators and Java-style iterators. The STL-style iterators are more low-level and more cumbersome to use; on the other hand, they are slightly faster and, for developers who already know STL, have the advantage of familiarity.

QMap<Key, T>::const_iterator allows you to iterate over a QMap (or a QMultiMap). If you want to modify the QMap as you iterate over it, you must use QMap::iterator instead. It is generally good practice to use QMap::const_iterator on a non-const QMap as well, unless you need to change the QMap through the iterator. Const iterators are slightly faster, and can improve code readability.

The default QMap::const_iterator constructor creates an uninitialized iterator. You must initialize it using a QMap function like QMap::constBegin(), QMap::constEnd(), or QMap::find() before you can start iterating. Here's a typical loop that prints all the (key, value) pairs stored in a map:

 QMap<QString, int> map;
 map.insert("January", 1);
 map.insert("February", 2);
 ...
 map.insert("December", 12);

 QMap<QString, int>::const_iterator i;
 for (i = map.constBegin(); i != map.constEnd(); ++i)
     cout << i.key() << ": " << i.value() << endl;

Unlike QHash, which stores its items in an arbitrary order, QMap stores its items ordered by key. Items that share the same key (because they were inserted using QMap::insertMulti()) will appear consecutively, from the most recently to the least recently inserted value.

Multiple iterators can be used on the same map. If you add items to the map, existing iterators will remain valid. If you remove items from the map, iterators that point to the removed items will become dangling iterators.

See also QMap::iterator and QMapIterator.


Member Type Documentation

typedef const_iterator::iterator_category

A synonym for std::bidirectional_iterator_tag indicating this iterator is a bidirectional iterator.


Member Function Documentation

const_iterator::const_iterator ()

Constructs an uninitialized iterator.

Functions like key(), value(), and operator++() must not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.

See also QMap::constBegin() and QMap::constEnd().

const_iterator::const_iterator ( const iterator & other )

Constructs a copy of other.

const Key & const_iterator::key () const

Returns the current item's key.

See also value().

const T & const_iterator::value () const

Returns the current item's value.

See also key() and operator*().

bool const_iterator::operator!= ( const const_iterator & other ) const

Returns true if other points to a different item than this iterator; otherwise returns false.

See also operator==().

const T & const_iterator::operator* () const

Returns the current item's value.

Same as value().

See also key().

const_iterator const_iterator::operator+ ( int j ) const

Returns an iterator to the item at j positions forward from this iterator. (If j is negative, the iterator goes backward.)

This operation can be slow for large j values.

See also operator-().

const_iterator & const_iterator::operator++ ()

The prefix ++ operator (++i) advances the iterator to the next item in the map and returns an iterator to the new current item.

Calling this function on QMap::end() leads to undefined results.

See also operator--().

const_iterator const_iterator::operator++ ( int )

This is an overloaded function.

The postfix ++ operator (i++) advances the iterator to the next item in the map and returns an iterator to the previously current item.

const_iterator & const_iterator::operator+= ( int j )

Advances the iterator by j items. (If j is negative, the iterator goes backward.)

This operation can be slow for large j values.

See also operator-=() and operator+().

const_iterator const_iterator::operator- ( int j ) const

Returns an iterator to the item at j positions backward from this iterator. (If j is negative, the iterator goes forward.)

This operation can be slow for large j values.

See also operator+().

const_iterator & const_iterator::operator-- ()

The prefix -- operator (--i) makes the preceding item current and returns an iterator pointing to the new current item.

Calling this function on QMap::begin() leads to undefined results.

See also operator++().

const_iterator const_iterator::operator-- ( int )

This is an overloaded function.

The postfix -- operator (i--) makes the preceding item current and returns an iterator pointing to the previously current item.

const_iterator & const_iterator::operator-= ( int j )

Makes the iterator go back by j items. (If j is negative, the iterator goes forward.)

This operation can be slow for large j values.

See also operator+=() and operator-().

const T * const_iterator::operator-> () const

Returns a pointer to the current item's value.

See also value().

bool const_iterator::operator== ( const const_iterator & other ) const

Returns true if other points to the same item as this iterator; otherwise returns false.

See also operator!=().

Publicité

Best Of

Actualités les plus lues

Semaine
Mois
Année
  1. « Quelque chose ne va vraiment pas avec les développeurs "modernes" », un développeur à "l'ancienne" critique la multiplication des bibliothèques 68
  2. Apercevoir la troisième dimension ou l'utilisation multithreadée d'OpenGL dans Qt, un article des Qt Quarterly traduit par Guillaume Belz 0
  3. Les développeurs ignorent-ils trop les failles découvertes dans leur code ? Prenez-vous en compte les remarques des autres ? 17
  4. BlackBerry 10 : premières images du prochain OS de RIM qui devrait intégrer des widgets et des tuiles inspirées de Windows Phone 0
  5. Quelles nouveautés de C++11 Visual C++ doit-il rapidement intégrer ? Donnez-nous votre avis 10
  6. Adieu qmake, bienvenue qbs : Qt Building Suite, un outil déclaratif et extensible pour la compilation de projets Qt 17
  7. La rubrique PyQt/PySide a besoin de vous ! 0
Page suivante

Le Qt Labs au hasard

Logo

Le moteur de rendu OpenGL

Les Qt Labs sont les laboratoires des développeurs de Qt, où ils peuvent partager des impressions sur le framework, son utilisation, ce que pourrait être son futur. Lire l'article.

Communauté

Ressources

Liens utiles

Contact

  • Vous souhaitez rejoindre la rédaction ou proposer un tutoriel, une traduction, une question... ? Postez dans le forum Contribuez ou contactez-nous par MP ou par email (voir en bas de page).

Qt dans le magazine

Cette page est une traduction d'une page de la documentation de Qt, écrite par Nokia Corporation and/or its subsidiary(-ies). Les éventuels problèmes résultant d'une mauvaise traduction ne sont pas imputables à Nokia. Qt 4.6
Copyright © 2012 Developpez LLC. Tous droits réservés Developpez LLC. Aucune reproduction, même partielle, ne peut être faite de ce site et de l'ensemble de son contenu : textes, documents et images sans l'autorisation expresse de Developpez LLC. Sinon, vous encourez selon la loi jusqu'à 3 ans de prison et jusqu'à 300 000 E de dommages et intérêts. Cette page est déposée à la SACD.
Vous avez déniché une erreur ? Un bug ? Une redirection cassée ? Ou tout autre problème, quel qu'il soit ? Ou bien vous désirez participer à ce projet de traduction ? N'hésitez pas à nous contacter ou par MP !
 
 
 
 
Partenaires

Hébergement Web