iterator Class▲
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Header: iterator
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qmake: QT += core
Detailed Description▲
QList 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.
QList<T>::iterator allows you to iterate over a QList<T> (or QQueue<T>) and to modify the list item associated with the iterator. If you want to iterate over a const QList, use QList::const_iterator instead. It is generally good practice to use QList::const_iterator on a non-const QList as well, unless you need to change the QList through the iterator. Const iterators are slightly faster, and can improve code readability.
The default QList::iterator constructor creates an uninitialized iterator. You must initialize it using a QList function like QList::begin(), QList::end(), or QList::insert() before you can start iterating. Here's a typical loop that prints all the items stored in a list:
QList<QString> list;
list.append("January");
list.append("February");
...
list.append("December");
QList<QString>::iterator i;
for (i = list.begin(); i != list.end(); ++i)
cout << *i << Qt::endl;Let's see a few examples of things we can do with a QList::iterator that we cannot do with a QList::const_iterator. Here's an example that increments every value stored in a QList<int> by 2:
QList<int>::iterator i;
for (i = list.begin(); i != list.end(); ++i)
*i += 2;Most QList functions accept an integer index rather than an iterator. For that reason, iterators are rarely useful in connection with QList. One place where STL-style iterators do make sense is as arguments to generic algorithms.
For example, here's how to delete all the widgets stored in a QList<QWidget *>:
QList<QWidget *> list;
...
qDeleteAll(list.begin(), list.end());Multiple iterators can be used on the same list. However, be aware that any non-const function call performed on the QList will render all existing iterators undefined. If you need to keep iterators over a long period of time, we recommend that you use QLinkedList rather than QList.
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 QList::const_iterator, QMutableListIterator
Member Type Documentation▲
iterator::iterator_category▲
A synonym for std::random_access_iterator_tag indicating this iterator is a random access iterator.
Member Function Documentation▲
bool iterator::operator==(const const_iterator &other) 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 iterator &other) const
Returns true if other points to a different item than this iterator; otherwise returns false.
See Also▲
See also operator==()
bool iterator::operator<(const const_iterator &other) const▲
bool iterator::operator<(const iterator &other) const
Returns true if the item pointed to by this iterator is less than the item pointed to by the other iterator.
bool iterator::operator<=(const const_iterator &other) const▲
bool iterator::operator<=(const iterator &other) const
Returns true if the item pointed to by this iterator is less than or equal to the item pointed to by the other iterator.
bool iterator::operator>(const const_iterator &other) const▲
bool iterator::operator>(const iterator &other) const
Returns true if the item pointed to by this iterator is greater than the item pointed to by the other iterator.
bool iterator::operator>=(const const_iterator &other) const▲
bool iterator::operator>=(const iterator &other) const
Returns true if the item pointed to by this iterator is greater than or equal to the item pointed to by the other iterator.
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 QList::begin(), QList::end()
iterator::iterator(const iterator &other)▲
Constructs a copy of other.
T &iterator::operator*() const▲
Returns a modifiable reference to the current item.
You can change the value of an item by using operator*() on the left side of an assignment, for example:
if (*it == "Hello")
*it = "Bonjour";See Also▲
See also operator->()
iterator iterator::operator+(iterator::difference_type j) const▲
Returns an iterator to the item at j positions forward from this iterator. (If j is negative, the iterator goes backward.)
See Also▲
See also operator-(), operator+=()
iterator &iterator::operator++()▲
The prefix ++ operator (++it) advances the iterator to the next item in the list and returns an iterator to the new current item.
Calling this function on QList::end() leads to undefined results.
See Also▲
See also operator--()
iterator iterator::operator++(int)▲
This is an overloaded function.
The postfix ++ operator (it++) advances the iterator to the next item in the list and returns an iterator to the previously current item.
iterator &iterator::operator+=(iterator::difference_type j)▲
Advances the iterator by j items. (If j is negative, the iterator goes backward.)
See Also▲
See also operator-=(), operator+()
iterator iterator::operator-(iterator::difference_type j) const▲
Returns an iterator to the item at j positions backward from this iterator. (If j is negative, the iterator goes forward.)
See Also▲
See also operator+(), operator-=()
int iterator::operator-(iterator other) const▲
Returns the number of items between the item pointed to by other and the item pointed to by this iterator.
iterator &iterator::operator--()▲
The prefix – operator (--it) makes the preceding item current and returns an iterator to the new current item.
Calling this function on QList::begin() leads to undefined results.
See Also▲
See also operator++()
iterator iterator::operator--(int)▲
This is an overloaded function.
The postfix – operator (it--) makes the preceding item current and returns an iterator to the previously current item.
iterator &iterator::operator-=(iterator::difference_type j)▲
Makes the iterator go back by j items. (If j is negative, the iterator goes forward.)
See Also▲
See also operator+=(), operator-()