QMapIterator Class

The QMapIterator class provides a Java-style const iterator for QMap and QMultiMap. More...

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

Public Functions

QMapIterator(const QMap<Key, T> &map)
QMapIterator<Key, T> &operator=(const QMap<Key, T> &container)
bool findNext(const T &value)
bool findPrevious(const T &value)
bool hasNext() const
bool hasPrevious() const
const Key &key() const
QMapIterator::Item next()
QMapIterator::Item peekNext() const
QMapIterator::Item peekPrevious() const
QMapIterator::Item previous()
void toBack()
void toFront()
const T &value() const

Detailed Description

QMap 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.

QMapIterator<Key, T> allows you to iterate over a QMap (or a QMultiMap). If you want to modify the map as you iterate over it, use QMutableMapIterator instead.

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

QMap<int, QWidget *> map;
...
QMapIterator<int, QWidget *> i(map);
while (i.hasNext()) {
    i.next();
    qDebug() << i.key() << ": " << i.value();
}

The next() function returns the next item in the map and advances the iterator. The key() and value() functions return the key and value of the last item that was jumped over.

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 so on.

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

QMapIterator<int, QWidget *> i(map);
i.toBack();
while (i.hasPrevious()) {
    i.previous();
    qDebug() << i.key() << ": " << i.value();
}

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

QMapIterator<int, QWidget *> i(map);
while (i.findNext(widget)) {
    qDebug() << "Found widget " << widget << " under key "
             << i.key();
}

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

See also QMutableMapIterator and QMap::const_iterator.

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