iterator Class
class QSet::iteratorThe QSet::iterator class provides an STL-style non-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
| iterator(const iterator &other) | |
| iterator() | |
| iterator & | operator=(const iterator &other) |
| bool | operator!=(const iterator &other) const |
| bool | operator!=(const const_iterator &other) const |
| const T & | operator*() const |
| iterator & | operator++() |
| iterator | operator++(int) |
| const T * | operator->() const |
| bool | operator==(const iterator &other) 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<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; set << "January" << "February" << ... << "December"; QSet<QString>::iterator i; for (i = set.begin(); i != set.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; set << "January" << "February" << ... << "December"; QSet<QString>::iterator 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
typedef iterator::iterator_category
Synonyms for std::bidirectional_iterator_tag indicating these iterators are bidirectional iterators.
Member Function Documentation
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.
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.
bool iterator::operator!=(const iterator &other) const
Returns true if other points to a different item than this iterator; otherwise returns false.
See also operator==().
bool iterator::operator!=(const const_iterator &other) const
bool iterator::operator==(const const_iterator &other) const
This is an overloaded function.
bool iterator::operator==(const iterator &other) const
Returns true if other points to the same item as this iterator; otherwise returns false.
See also operator!=().
const T *iterator::operator->() const
Returns a pointer to the current item.
See also operator*().
const T &iterator::operator*() const
Returns a reference to the current item.
See also operator->().
iterator &iterator::operator=(const iterator &other)
Assigns other to this iterator.
iterator::iterator(const iterator &other)
Constructs a copy of other.
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().