iterator Class▲
-
Header: iterator
-
CMake:
find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core)
-
qmake: QT += core
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.
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▲
See also QSet::const_iterator, 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▲
See also QSet::begin(), QSet::end()
iterator::iterator(const iterator &other)▲
Constructs a copy of other.
iterator &iterator::operator=(const iterator &other)▲
Assigns other to this iterator.
const T &iterator::operator*() const▲
const T *iterator::operator->() const▲
bool iterator::operator==(const iterator &other) const▲
Returns true if other points to the same item as this iterator; otherwise returns false.
See Also▲
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 a different item than this iterator; otherwise returns false.
See Also▲
See also operator==()
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.
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.