QListIterator Class

The QListIterator class provides a Java-style const iterator for QList and QQueue. More...

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

Public Functions

QListIterator(const QList<T> &list)
QListIterator<T> &operator=(const QList<T> &container)
bool findNext(const T &value)
bool findPrevious(const T &value)
bool hasNext() const
bool hasPrevious() const
const T &next()
const T &peekNext() const
const T &peekPrevious() const
const T &previous()
void toBack()
void toFront()

Detailed Description

QList has both Java-style iterators and STL-style iterators. The Java-style iterators are more high-level and easier to use than the STL-style iterators; on the other hand, they are slightly less efficient.

An alternative to using iterators is to use index positions. Most QList member functions take an index as their first parameter, making it possible to access, modify, and remove items without using iterators.

QListIterator<T> allows you to iterate over a QList<T> (or a QQueue<T>). If you want to modify the list as you iterate over it, use QMutableListIterator<T> instead.

The QListIterator constructor takes a QList as argument. After construction, the iterator is located at the very beginning of the list (before the first item). Here's how to iterate over all the elements sequentially:

QList<float> list;
QListIterator<float> i(list);
while (i.hasNext())
    qDebug() << i.next();

The next() function returns the next item in the list and advances the iterator. Unlike STL-style iterators, Java-style iterators point between items rather than directly at items. The first call to next() advances the iterator to the position between the first and second item, and returns the first item; the second call to next() advances the iterator to the position between the second and third item, and returns the second item; and so on.

Here's how to iterate over the elements in reverse order:

QListIterator<float> i(list);
while (i.hasPrevious())
    qDebug() << i.previous();

If you want to find all occurrences of a particular value, use findNext() or findPrevious() in a loop.

Multiple iterators can be used on the same list. If the list is modified while a QListIterator is active, the QListIterator will continue iterating over the original list, ignoring the modified copy.

See also QMutableListIterator and QList::const_iterator.

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