QMutableLinkedListIterator Class

The QMutableLinkedListIterator class provides a Java-style non-const iterator for QLinkedList. More...

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

Public Functions

QMutableLinkedListIterator(QLinkedList<T> &list)
QMutableLinkedListIterator<T> &operator=(QLinkedList<T> &container)
bool findNext(const T &value)
bool findPrevious(const T &value)
bool hasNext() const
bool hasPrevious() const
void insert(const T &value)
T &next()
T &peekNext() const
T &peekPrevious() const
T &previous()
void remove()
void setValue(const T &value) const
void toBack()
void toFront()
const T &value() const
T &value()

Detailed Description

QLinkedList 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.

QMutableLinkedListIterator<T> allows you to iterate over a QLinkedList<T> and modify the list. If you don't want to modify the list (or have a const QLinkedList), use the slightly faster QLinkedListIterator<T> instead.

The QMutableLinkedListIterator constructor takes a QLinkedList 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:

QLinkedList<float> list;
...
QMutableLinkedListIterator<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, returning the second item; and so on.

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

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

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

If you want to remove items as you iterate over the list, use remove(). If you want to modify the value of an item, use setValue(). If you want to insert a new item in the list, use insert().

Example:

QMutableLinkedListIterator<int> i(list);
while (i.hasNext()) {
    int val = i.next();
    if (val < 0) {
        i.setValue(-val);
    } else if (val == 0) {
        i.remove();
    }
}

The example traverses a list, replacing negative numbers with their absolute values, and eliminating zeroes.

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

See also QLinkedListIterator and QLinkedList::iterator.

Member Function Documentation

void QMutableLinkedListIterator::remove()

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

Example:

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

See also insert() and setValue().

void QMutableLinkedListIterator::setValue(const T &value) const

Replaces the value of the last item that was jumped over using one of the traversal functions with value.

The traversal functions are next(), previous(), findNext(), and findPrevious().

Example:

QMutableLinkedListIterator<double> i(list);
while (i.hasNext()) {
    double val = i.next();
    i.setValue(std::sqrt(val));
}

See also value(), remove(), and insert().

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