iterator Class Reference
(QList::iterator)
[QtCore module]

Detailed Description

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

QList 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.

QList<T>::iterator allows you to iterate over a QList<T> (or QQueue<T>) and to modify the list item associated with the iterator. If you want to iterate over a const QList, use QList::const_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::iterator constructor creates an uninitialized iterator. You must initialize it using a QList function like QList::begin(), QList::end(), 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>::iterator i;
 for (i = list.begin(); i != list.end(); ++i)
     cout << *i << endl;

Let's see a few examples of things we can do with a QList::iterator that we cannot do with a QList::const_iterator. Here's an example that increments every value stored in a QList<int> by 2:

 QList<int>::iterator i;
 for (i = list.begin(); i != list.end(); ++i)
     *i += 2;

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.begin(), list.end());

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.

See also QList::const_iterator and QMutableListIterator.

Member Type Documentation

 if (*it == "Hello")
     *it = "Bonjour";