const_iterator Class

class QSet::const_iterator

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

Public Types

Public Functions

const_iterator(const iterator &other)
const_iterator(const const_iterator &other)
const_iterator()
const_iterator &operator=(const const_iterator &other)
bool operator!=(const const_iterator &other) const
const T &operator*() const
const_iterator &operator++()
const_iterator operator++(int)
const T *operator->() const
bool operator==(const 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<Key, T>::const_iterator allows you to iterate over a QSet. If you want to modify the QSet as you iterate over it, you must use QSet::iterator instead. 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::const_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;
set << "January" << "February" << ... << "December";

QSet<QString>::const_iterator i;
for (i = set.begin(); i != set.end(); ++i)
    qDebug() << *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>::const_iterator it = std::find_if(set.cbegin(), set.cend(), predicate);
if (it != set.constEnd())
    cout << "Found Jeanette" << endl;

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::iterator and QSetIterator.

Member Type Documentation

const_iterator::iterator_category

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

Member Function Documentation

const_iterator const_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.

const_iterator &const_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.

bool const_iterator::operator!=(const const_iterator &other) const

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

See also operator==().

bool const_iterator::operator==(const const_iterator &other) const

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

See also operator!=().

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

Returns a pointer to the current item.

See also operator*().

const T &const_iterator::operator*() const

Returns a reference to the current item.

See also operator->().

const_iterator &const_iterator::operator=(const const_iterator &other)

Assigns other to this iterator.

const_iterator::const_iterator(const const_iterator &other)

Constructs a copy of other.

const_iterator::const_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().

const_iterator::const_iterator(const iterator &other)

This is an overloaded function.

Constructs a copy of other.

© 2021 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.