Qt 4.3: QList::iterator Class Reference

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# QList::iterator Class Reference
[QtCore module]

The QList::iterator class provides an STL-style non-const iterator for QList and QQueue. More...

     #include <QList>

- List of all members, including inherited members

### 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+ ( int j ) const
- iterator & operator++ ()
- iterator operator++ ( int )
- iterator & operator+= ( int j )
- iterator operator- ( int j ) const
- int operator- ( iterator other ) const
- iterator & operator-- ()
- iterator operator-- ( int )
- iterator & operator-= ( int 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[] ( int 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.

See also QList::const_iterator and QMutableListIterator.

## Member Function Documentation

### iterator::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::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

This is an overloaded member function, provided for convenience.

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+ ( 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+=().

### 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 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.

### iterator & iterator::operator+= ( int j )

Advances the iterator by j items. (If j is negative, the iterator goes backward.)

See also operator-=() and operator+().

### iterator 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 iterator::operator- ( 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.

### 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 member function, provided for convenience.

The postfix -- operator (`it--`) makes the preceding item current and returns an iterator to the previously current item.

### iterator & 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-().

### 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

This is an overloaded member function, provided for convenience.

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

This is an overloaded member function, provided for convenience.

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

This is an overloaded member function, provided for convenience.

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

This is an overloaded member function, provided for convenience.

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

This is an overloaded member function, provided for convenience.

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[] ( int 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+().