const_iterator Class

(QList::const_iterator)

The QList::const_iterator class provides an STL-style const iterator for QList and QQueue. More...

Header: #include <const_iterator>
qmake: QT += core

Public Types

Public Functions

Public Variables

QList::Node *i

Detailed Description

The QList::const_iterator class provides an STL-style const iterator for QList and QQueue.

QList provides 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.

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

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


  QList<QString> list;
  list.append("January");
  list.append("February");
  ...
  list.append("December");

  QList<QString>::const_iterator i;
  for (i = list.constBegin(); i != list.constEnd(); ++i)
      cout << *i << endl;

Most QList functions accept an integer index rather than an iterator. For that reason, iterators are rarely useful in connection with QList. One place where STL-style iterators do make sense is as arguments to generic algorithms.

For example, here's how to delete all the widgets stored in a QList<QWidget *>:


  QList<QWidget *> list;
  ...
  qDeleteAll(list.constBegin(), list.constEnd());

Multiple iterators can be used on the same list. However, be aware that any non-const function call performed on the QList will render all existing iterators undefined. If you need to keep iterators over a long period of time, we recommend that you use QLinkedList rather than QList.

Warning: Iterators on implicitly shared containers do not work exactly like STL-iterators. You should avoid copying a container while iterators are active on that container. For more information, read Implicit sharing iterator problem.

See also QList::iterator and QListIterator.

Member Type Documentation

typedef const_iterator::iterator_category

A synonym for std::random_access_iterator_tag indicating this iterator is a random access iterator.

Member Function Documentation

const_iterator::const_iterator()

Default constructs an instance of const_iterator.