iterator Class

class QSet::iterator

The QSet::iterator class provides an STL-style non-const iterator for QSet. More...

Public Types

Public Functions

iterator()
iterator(const QSet<T>::iterator &other)
bool operator!=(const QSet<T>::iterator &other) const
bool operator!=(const QSet<T>::const_iterator &other) const
const T &operator*() const
QSet<T>::iterator &operator++()
QSet<T>::iterator operator++(int)
const T *operator->() const
QSet<T>::iterator &operator=(const QSet<T>::iterator &other)
bool operator==(const QSet<T>::iterator &other) const
bool operator==(const QSet<T>::const_iterator &other) const

Detailed Description

QSet 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.

QSet<T>::iterator allows you to iterate over a QSet and to remove items (using QSet::erase()) while you iterate. (QSet doesn't let you modify a value through an iterator, because that would potentially require moving the value in the internal hash table used by QSet.) If you want to iterate over a const QSet, you should use QSet::const_iterator. It is generally good practice to use QSet::const_iterator on a non-const QSet as well, unless you need to change the QSet through the iterator. Const iterators are slightly faster, and can improve code readability.

The default QSet::iterator constructor creates an uninitialized iterator. You must initialize it using a function like QSet::begin(), QSet::end(), or QSet::insert() before you can start iterating. Here's a typical loop that prints all the items stored in a set:

QSet<QString> set = {"January", "February", ... "December"}

// i is a QSet<QString>::iterator
for (auto i = set.begin(), end = set.end(); i != end; ++i)
    qDebug() << *i;

Here's a loop that removes certain items (all those that start with 'J') from a set while iterating:

QSet<QString> set = {"January", "February", ... "December"};

auto i = set.begin();
while (i != set.end()) {
    if ((*i).startsWith('J')) {
        i = set.erase(i);
    } else {
        ++i;
    }
}

STL-style iterators can be used as arguments to generic algorithms. For example, here's how to find an item in the set using the qFind() algorithm:

QSet<QString> set;
...
const auto predicate = [](const QString &s) { return s.compare("Jeanette", Qt::CaseInsensitive) == 0; };
QSet<QString>::iterator it = std::find_if(set.begin(), set.end(), predicate);
if (it != set.end())
    cout << "Found Jeanette" << endl;

Multiple iterators can be used on the same set.

Warning: Iterators on implicitly shared containers do not work exactly like STL-iterators. You should avoid copying a container while iterators are active on that container. For more information, read Implicit sharing iterator problem.

See also QSet::const_iterator and QMutableSetIterator.

Member Type Documentation

iterator::iterator_category

Synonyms for std::bidirectional_iterator_tag indicating these iterators are bidirectional iterators.

Member Function Documentation

iterator::iterator()

Constructs an uninitialized iterator.

Functions like operator*() and operator++() should not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.

See also QSet::begin() and QSet::end().

iterator::iterator(const QSet<T>::iterator &other)

Constructs a copy of other.

QSet<T>::iterator &iterator::operator=(const QSet<T>::iterator &other)

Assigns other to this iterator.

const T &iterator::operator*() const

Returns a reference to the current item.

See also operator->().

const T *iterator::operator->() const

Returns a pointer to the current item.

See also operator*().

bool iterator::operator==(const QSet<T>::iterator &other) const

Returns true if other points to the same item as this iterator; otherwise returns false.

See also operator!=().

bool iterator::operator!=(const QSet<T>::const_iterator &other) const

bool iterator::operator==(const QSet<T>::const_iterator &other) const

This is an overloaded function.

bool iterator::operator!=(const QSet<T>::iterator &other) const

Returns true if other points to a different item than this iterator; otherwise returns false.

See also operator==().

QSet<T>::iterator &iterator::operator++()

The prefix ++ operator (++it) advances the iterator to the next item in the set and returns an iterator to the new current item.

Calling this function on QSet<T>::constEnd() leads to undefined results.

QSet<T>::iterator iterator::operator++(int)

This is an overloaded function.

The postfix ++ operator (it++) advances the iterator to the next item in the set and returns an iterator to the previously current item.

© 2024 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.