- Qt 6.9
- Qt 5 Core Compatibility APIs
- C++ Classes
- const_iterator
- Qt 6.9.1 Reference Documentation

# QLinkedList::const_iterator Class

class QLinkedList::const_iterator

The QLinkedList::const_iterator class provides an STL-style const iterator for QLinkedList. More...

- List of all members, including inherited members

## Public Functions

| const_iterator()
| const_iterator(QLinkedList<T>::iterator other)
bool | operator!=(const QLinkedList<T>::const_iterator &other) const
const T & | operator*() const
QLinkedList<T>::const_iterator | operator+(int j) const
QLinkedList<T>::const_iterator & | operator++()
QLinkedList<T>::const_iterator | operator++(int)
QLinkedList<T>::const_iterator & | operator+=(int j)
QLinkedList<T>::const_iterator | operator-(int j) const
QLinkedList<T>::const_iterator & | operator--()
QLinkedList<T>::const_iterator | operator--(int)
QLinkedList<T>::const_iterator & | operator-=(int j)
const T * | operator->() const
bool | operator==(const QLinkedList<T>::const_iterator &other) const

## Detailed Description

QLinkedList 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.

QLinkedList<T>::const_iterator allows you to iterate over a QLinkedList<T>. If you want modify the QLinkedList as you iterate over it, you must use QLinkedList::iterator instead. It is generally good practice to use QLinkedList::const_iterator on a non-const QLinkedList as well, unless you need to change the QLinkedList through the iterator. Const iterators are slightly faster, and can improve code readability.

The default QLinkedList::const_iterator constructor creates an uninitialized iterator. You must initialize it using a function like QLinkedList::constBegin(), QLinkedList::constEnd(), or QLinkedList::insert() before you can start iterating. Here's a typical loop that prints all the items stored in a list:

     QLinkedList<QString> list;
     list.append("January");
     list.append("February");
     ...
     list.append("December");

     QLinkedList<QString>::const_iterator i;
     for (i = list.constBegin(); i != list.constEnd(); ++i)
         cout << *i << Qt::endl;

STL-style iterators can be used as arguments to generic algorithms. For example, here's how to find an item in the list:

     QLinkedList<QString> list;
     ...
     QLinkedList<QString>::const_iterator it = std::find(list.constBegin(),
                                                         list.constEnd(), "Joel");
     if (it != list.constEnd())
         cout << "Found Joel" << Qt::endl;

Multiple iterators can be used on the same list. If you add items to the list, existing iterators will remain valid. If you remove items from the list, iterators that point to the removed items will become dangling iterators.

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 QLinkedList::iterator and QLinkedListIterator.

## 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 QLinkedList::constBegin() and QLinkedList::constEnd().

### const_iterator::const_iterator(QLinkedList<T>::iterator other)

Constructs a copy of other.

### bool const_iterator::operator!=(const QLinkedList<T>::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 a reference to the current item.

See also operator->().

### QLinkedList<T>::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.)

This operation can be slow for large j values.

See also operator-().

### QLinkedList<T>::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 QLinkedList<T>::constEnd() leads to undefined results.

See also operator--().

### QLinkedList<T>::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.

### QLinkedList<T>::const_iterator &const_iterator::operator+=(int j)

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

This operation can be slow for large j values.

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

### QLinkedList<T>::const_iterator const_iterator::operator-(int j) const

This function returns an iterator to the item at j positions backward from this iterator. (If j is negative, the iterator goes forward.)

This operation can be slow for large j values.

See also operator+().

### QLinkedList<T>::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 QLinkedList::begin() leads to undefined results.

See also operator++().

### QLinkedList<T>::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.

### QLinkedList<T>::const_iterator &const_iterator::operator-=(int j)

Makes the iterator go back by j items. (If j is negative, the iterator goes forward.)

This operation can be slow for large j values.

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 QLinkedList<T>::const_iterator &other) const

Returns `true` if other points to the same item as this iterator; otherwise returns `false`.

See also operator!=().