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

typedef const_iterator::iterator_category

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.