const_iterator Class

Class const_iterator is declared in class QSet.

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

This class was introduced in Qt 4.2.

Public Types

typedef difference_type
typedef iterator_category
typedef pointer
typedef reference
typedef value_type

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+(int j) const
const_iterator &operator++()
const_iterator operator++(int)
const_iterator &operator+=(int j)
const_iterator operator-(int j) const
const_iterator &operator--()
const_iterator operator--(int)
const_iterator &operator-=(int j)
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

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

Member Function Documentation

const_iterator::const_iterator(const iterator &other)

This is an overloaded function.

Constructs a copy of other.

This function was introduced in Qt 4.2.

© 2019 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.