iterator Class
(QList::iterator)The QList::iterator class provides an STL-style non-const iterator for QList and QQueue. More...
| Header: | #include <iterator> |
| qmake: | QT += core |
Public Types
| typedef | iterator_category |
Public Functions
| iterator() | |
| iterator(const iterator &other) | |
| bool | operator!=(const iterator &other) const |
| bool | operator!=(const const_iterator &other) const |
| T & | operator*() const |
| iterator | operator+(difference_type j) const |
| iterator & | operator++() |
| iterator | operator++(int) |
| iterator & | operator+=(difference_type j) |
| iterator | operator-(difference_type j) const |
| int | operator-(iterator other) const |
| iterator & | operator--() |
| iterator | operator--(int) |
| iterator & | operator-=(difference_type j) |
| T * | operator->() const |
| bool | operator<(const iterator &other) const |
| bool | operator<(const const_iterator &other) const |
| bool | operator<=(const iterator &other) const |
| bool | operator<=(const const_iterator &other) const |
| bool | operator==(const iterator &other) const |
| bool | operator==(const const_iterator &other) const |
| bool | operator>(const iterator &other) const |
| bool | operator>(const const_iterator &other) const |
| bool | operator>=(const iterator &other) const |
| bool | operator>=(const const_iterator &other) const |
| T & | operator[](difference_type j) const |
Detailed Description
The QList::iterator class provides an STL-style non-const iterator for QList and QQueue.
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 << 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.
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 QList::const_iterator and QMutableListIterator.
Member Type Documentation
typedef iterator::iterator_category
A synonym for std::random_access_iterator_tag indicating this iterator is a random access iterator.
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 QList::begin() and QList::end().
iterator::iterator(const iterator &other)
Constructs a copy of other.
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
Returns true if other points to a different item than this iterator; otherwise returns false.
See also operator==().
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 operator->().
iterator iterator::operator+(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 operator-() and 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 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+=(difference_type j)
Advances the iterator by j items. (If j is negative, the iterator goes backward.)
See also operator-=() and operator+().
iterator iterator::operator-(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 operator+() and 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 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-=(difference_type j)
Makes the iterator go back by j items. (If j is negative, the iterator goes forward.)
See also operator+=() and operator-().
T *iterator::operator->() const
Returns a pointer to the current item.
See also operator*().
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
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 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
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 iterator &other) const
Returns true if other points to the same item as this iterator; otherwise returns false.
See also operator!=().
bool iterator::operator==(const const_iterator &other) const
Returns true if other points to the same item as this iterator; otherwise returns false.
See also operator!=().
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
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 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.
bool iterator::operator>=(const 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.
T &iterator::operator[](difference_type j) const
Returns a modifiable reference to the item at position *this + j.
This function is provided to make QList iterators behave like C++ pointers.
See also operator+().
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