Detailed Description
The QList::const_iterator class provides an STL-style const iterator for QList and QQueue.
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 << 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.
Member Function Documentation
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().
const_iterator::const_iterator ( const const_iterator & other )
Constructs a copy of other.
const_iterator::const_iterator ( const iterator & other )
Constructs a copy of other.
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+ ( int 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+= ( int 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- ( int 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-= ( int 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[] ( int j ) const
Returns the item at position *this + j.
This function is provided to make QList iterators behave like C++ pointers.
See also operator+().
