QMutableSetIterator Class

The QMutableSetIterator class provides a Java-style non-const iterator for QSet. More...

Header: #include <QMutableSetIterator>
qmake: QT += core
Since: Qt 4.2

This class was introduced in Qt 4.2.

Public Functions

QMutableSetIterator(QSet<T> &set)
QMutableSetIterator<T> &operator=(QSet<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 remove()
void toBack()
void toFront()
const T &value() const

Detailed Description

QSet 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.

QMutableSetIterator<T> allows you to iterate over a QSet<T> and remove items from the set as you iterate. If you don't want to modify the set (or have a const QSet), use the slightly faster QSetIterator<T> instead.

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

QSet<float> set;
...
QMutableSetIterator<float> i(set);
while (i.hasNext())
    qDebug() << i.next();

The next() function returns the next item in the set 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, returning the second item; and so on.

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

QMutableSetIterator<float> i(set);
i.toBack();
while (i.hasPrevious())
    qDebug() << i.previous();

If you want to remove items as you iterate over the set, use remove().

Only one mutable iterator can be active on a given set at any time. Furthermore, no changes should be done directly to the set while the iterator is active (as opposed to through the iterator), since this could invalidate the iterator and lead to undefined behavior.

See also QSetIterator and QSet::iterator.

Member Function Documentation

void QMutableSetIterator::remove()

Removes the last item that was jumped over using one of the traversal functions (next(), previous(), findNext(), findPrevious()).

Example:

QMutableSetIterator<int> i(set);
while (i.hasNext()) {
    int val = i.next();
    if (val < -32768 || val > 32767)
        i.remove();
}

See also value().

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