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.
See also QList::iterator and QListIterator.
Member Function Documentation
const_iterator::const_iterator ()
Constructs an uninitialized iterator.
Functions like operator*() and operator++() should not be called on an uninitialized iterartor. 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 member function, provided for convenience.
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
This is an overloaded member function, provided for convenience.
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 member function, provided for convenience.
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+().
