const_iterator Class
class QList::const_iteratorThe QList::const_iterator class provides an STL-style const iterator for QList and QQueue. More...
Public Types
| typedef | iterator_category |
Public Functions
| const_iterator(const iterator &other) | |
| const_iterator(const const_iterator &other) | |
| const_iterator() | |
| bool | operator!=(const const_iterator &other) const |
| const T & | operator*() const |
| const_iterator | operator+(difference_type j) const |
| const_iterator & | operator++() |
| const_iterator | operator++(int) |
| const_iterator & | operator+=(difference_type j) |
| const_iterator | operator-(difference_type j) const |
| int | operator-(const_iterator other) const |
| const_iterator & | operator--() |
| const_iterator | operator--(int) |
| const_iterator & | operator-=(difference_type j) |
| const T * | operator->() const |
| bool | operator<(const const_iterator &other) const |
| bool | operator<=(const const_iterator &other) const |
| bool | operator==(const const_iterator &other) const |
| bool | operator>(const const_iterator &other) const |
| bool | operator>=(const const_iterator &other) const |
| const T & | operator[](difference_type j) const |
Detailed Description
QList provides 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>::const_iterator allows you to iterate over a QList<T> (or a QQueue<T>). If you want to modify the QList as you iterate over it, use QList::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::const_iterator constructor creates an uninitialized iterator. You must initialize it using a QList function like QList::constBegin(), QList::constEnd(), 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>::const_iterator i; for (i = list.constBegin(); i != list.constEnd(); ++i) cout << *i << Qt::endl;
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.constBegin(), list.constEnd());
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::iterator and QListIterator.
Member Type Documentation
typedef const_iterator::iterator_category
A synonym for std::random_access_iterator_tag indicating this iterator is a random access iterator.
Member Function Documentation
const_iterator::const_iterator(const iterator &other)
Constructs a copy of other.
const_iterator::const_iterator(const const_iterator &other)
Constructs a copy of other.
const_iterator::const_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::constBegin() and QList::constEnd().
bool const_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==().
const T &const_iterator::operator*() const
Returns the current item.
See also operator->().
const_iterator const_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+=().
const_iterator &const_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--().
const_iterator const_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.
const_iterator &const_iterator::operator+=(difference_type j)
Advances the iterator by j items. (If j is negative, the iterator goes backward.)
See also operator-=() and operator+().
const_iterator const_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 const_iterator::operator-(const_iterator other) const
Returns the number of items between the item pointed to by other and the item pointed to by this iterator.
const_iterator &const_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++().
const_iterator const_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.
const_iterator &const_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-().
const T *const_iterator::operator->() const
Returns a pointer to the current item.
See also operator*().
bool const_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 const_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 const_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 const_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 const_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.
const T &const_iterator::operator[](difference_type j) const
Returns the item at position *this + j.
This function is provided to make QList iterators behave like C++ pointers.
See also operator+().