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# QLinkedList Class Reference

The QLinkedList class is a template class that provides linked lists. More...

    #include <QLinkedList>

Note: All the functions in this class are reentrant.

- List of all members, including inherited members
- Compatibility members

### Public Types

- class const_iterator
- class iterator
- typedef ConstIterator
- typedef Iterator

### Public Functions

- QLinkedList ()
- QLinkedList ( const QLinkedList & other )
- ~QLinkedList ()
- void append ( const T & value )
- T & back ()
- const T & back () const
- iterator begin ()
- const_iterator begin () const
- void clear ()
- const_iterator constBegin () const
- const_iterator constEnd () const
- bool contains ( const T & value ) const
- int count ( const T & value ) const
- int count () const
- bool empty () const
- iterator end ()
- const_iterator end () const
- iterator erase ( iterator pos )
- iterator erase ( iterator begin, iterator end )
- T & first ()
- const T & first () const
- T & front ()
- const T & front () const
- iterator insert ( iterator before, const T & value )
- bool isEmpty () const
- T & last ()
- const T & last () const
- void pop_back ()
- void pop_front ()
- void prepend ( const T & value )
- void push_back ( const T & value )
- void push_front ( const T & value )
- int removeAll ( const T & value )
- void removeFirst ()
- void removeLast ()
- int size () const
- T takeFirst ()
- T takeLast ()
- bool operator!= ( const QLinkedList & other ) const
- QLinkedList operator+ ( const QLinkedList & other ) const
- QLinkedList & operator+= ( const QLinkedList & other )
- void operator+= ( const T & value )
- QLinkedList & operator<< ( const T & value )
- QLinkedList<T> & operator= ( const QLinkedList & other )
- bool operator== ( const QLinkedList & other ) const

### Related Non-Members

- QDataStream & operator<< ( QDataStream & out, const QLinkedList<T> & list )
- QDataStream & operator>> ( QDataStream & in, QLinkedList<T> & list )

## Detailed Description

The QLinkedList class is a template class that provides linked lists.

QLinkedList<T> is one of Qt's generic container classes. It stores a list of values and provides iterator-based access as well as constant time insertions and removals.

QList<T>, QLinkedList<T>, and QVector<T> provide similar functionality. Here's an overview:

- For most purposes, QList is the right class to use. Its index-based API is more convenient than QLinkedList's iterator-based API, and it is usually faster than QVector because of the way it stores its items in memory. It also expands to less code in your executable.
- If you need a real linked list, with guarantees of constant time insertions in the middle of the list and iterators to items rather than indexes, use QLinkedList.
- If you want the items to occupy adjacent memory positions, use QVector.

Here's an example of a QLinkedList that stores integers and a QLinkedList that stores QTime values:

        QLinkedList<int> integerList;
        QLinkedList<QTime> timeList;

QLinkedList stores a list of items. The default constructor creates an empty list. To insert items into the list, you can use operator<<():

        QLinkedList<QString> list;
        list << "one" << "two" << "three";
        // list: ["one", "two", "three"]

If you want to get the first or last item in a linked list, use first() or last(). If you want to remove an item from either end of the list, use removeFirst() or removeLast(). If you want to remove all occurrences of a given value in the list, use removeAll().

A common requirement is to remove the first or last item in the list and do something with it. For this, QLinkedList provides takeFirst() and takeLast(). Here's a loop that removes the items from a list one at a time and calls `delete` on them:

        QLinkedList<QWidget *> list;
        ...
        while (!list.isEmpty())
            delete list.takeFirst();

QLinkedList's value type must be an assignable data type. This covers most data types that are commonly used, but the compiler won't let you, for example, store a QWidget as a value; instead, store a QWidget *. A few functions have additional requirements; for example, contains() and removeAll() expect the value type to support `operator==()`. These requirements are documented on a per-function basis.

If you want to insert, modify, or remove items in the middle of the list, you must use an iterator. QLinkedList provides both Java-style iterators (QLinkedListIterator and QLinkedListMutableIterator) and STL-style iterators (QLinkedList::const_iterator and QLinkedList::iterator). See the documentation for these classes for details.

See also QListIterator, QListMutableIterator, QList, and QVector.

## Member Type Documentation

### typedef QLinkedList::ConstIterator

Qt-style synonym for QList::const_iterator.

### typedef QLinkedList::Iterator

Qt-style synonym for QList::iterator.

## Member Function Documentation

### QLinkedList::QLinkedList ()

Constructs an empty list.

### QLinkedList::QLinkedList ( const QLinkedList & other )

Constructs a copy of other.

This operation occurs in constant time, because QLinkedList is implicitly shared. This makes returning a QLinkedList from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and this takes linear time.

See also operator=().

### QLinkedList::~QLinkedList ()

Destroys the list. References to the values in the list, and all iterators over this list, become invalid.

### void QLinkedList::append ( const T & value )

Inserts value at the end of the list.

Example:

        QLinkedList<QString> list;
        list.append("one");
        list.append("two");
        list.append("three");
        // list: ["one", "two", "three"]

This is the same as list.insert(end(), value).

See also operator<<(), prepend(), and insert().

### T & QLinkedList::back ()

This function is provided for STL compatibility. It is equivalent to last().

### const T & QLinkedList::back () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

### iterator QLinkedList::begin ()

Returns an STL-style iterator pointing to the first item in the list.

See also constBegin() and end().

### const_iterator QLinkedList::begin () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

### void QLinkedList::clear ()

Removes all the items in the list.

See also removeAll().

### const_iterator QLinkedList::constBegin () const

Returns a const STL-style iterator pointing to the first item in the list.

See also begin() and constEnd().

### const_iterator QLinkedList::constEnd () const

Returns a const STL-style iterator pointing to the imaginary item after the last item in the list.

See also constBegin() and end().

### bool QLinkedList::contains ( const T & value ) const

Returns true if the list contains an occurrence of value; otherwise returns false.

This function requires the value type to have an implementation of `operator==()`.

See also QListIterator::findNext() and QListIterator::findPrevious().

### int QLinkedList::count ( const T & value ) const

Returns the number of occurrences of value in the list.

This function requires the value type to have an implementation of `operator==()`.

See also contains().

### int QLinkedList::count () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Same as size().

### bool QLinkedList::empty () const

This function is provided for STL compatibility. It is equivalent to isEmpty().

### iterator QLinkedList::end ()

Returns an STL-style iterator pointing to the imaginary item after the last item in the list.

See also begin() and constEnd().

### const_iterator QLinkedList::end () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

### iterator QLinkedList::erase ( iterator pos )

Removes the item pointed to by the iterator pos from the list, and returns an iterator to the next item in the list (which may be end()).

See also insert().

### iterator QLinkedList::erase ( iterator begin, iterator end )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Removes all the items from begin up to (but not including) end.

### T & QLinkedList::first ()

Returns a reference to the first item in the list. This function assumes that the list isn't empty.

See also last() and isEmpty().

### const T & QLinkedList::first () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

### T & QLinkedList::front ()

This function is provided for STL compatibility. It is equivalent to first().

### const T & QLinkedList::front () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

### iterator QLinkedList::insert ( iterator before, const T & value )

Inserts value in front of the item pointed to by the iterator before. Returns an iterator pointing at the inserted item.

See also erase().

### bool QLinkedList::isEmpty () const

Returns true if the list contains no items; otherwise returns false.

See also size().

### T & QLinkedList::last ()

Returns a reference to the last item in the list. This function assumes that the list isn't empty.

See also first() and isEmpty().

### const T & QLinkedList::last () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

### void QLinkedList::pop_back ()

This function is provided for STL compatibility. It is equivalent to removeLast().

### void QLinkedList::pop_front ()

This function is provided for STL compatibility. It is equivalent to removeFirst().

### void QLinkedList::prepend ( const T & value )

Inserts value at the beginning of the list.

Example:

        QLinkedList<QString> list;
        list.prepend("one");
        list.prepend("two");
        list.prepend("three");
        // list: ["three", "two", "one"]

This is the same as list.insert(begin(), value).

See also append() and insert().

### void QLinkedList::push_back ( const T & value )

This function is provided for STL compatibility. It is equivalent to append(value).

### void QLinkedList::push_front ( const T & value )

This function is provided for STL compatibility. It is equivalent to prepend(value).

### int QLinkedList::removeAll ( const T & value )

Removes all occurrences of value in the list.

Example:

        QList<QString> list;
        list << "sun" << "cloud" << "sun" << "rain";
        list.removeAll("sun");
        // list: ["cloud", "rain"]

This function requires the value type to have an implementation of `operator==()`.

See also insert().

### void QLinkedList::removeFirst ()

Removes the first item in the list.

This is the same as erase(begin()).

See also removeLast() and erase().

### void QLinkedList::removeLast ()

Removes the last item in the list.

See also removeFirst() and erase().

### int QLinkedList::size () const

Returns the number of items in the list.

See also isEmpty() and count().

### T QLinkedList::takeFirst ()

Removes the first item in the list and returns it.

If you don't use the return value, removeFirst() is more efficient.

See also takeLast() and removeFirst().

### T QLinkedList::takeLast ()

Removes the last item in the list and returns it.

If you don't use the return value, removeLast() is more efficient.

See also takeFirst() and removeLast().

### bool QLinkedList::operator!= ( const QLinkedList & other ) const

Returns true if other is not equal to this list; otherwise returns false.

Two lists are considered equal if they contain the same values in the same order.

This function requires the value type to implement `operator==()`.

See also operator==().

### QLinkedList QLinkedList::operator+ ( const QLinkedList & other ) const

Returns a list that contains all the items in this list followed by all the items in the other list.

See also operator+=().

### QLinkedList & QLinkedList::operator+= ( const QLinkedList & other )

Appends the items of the other list to this list and returns a reference to this list.

See also operator+() and append().

### void QLinkedList::operator+= ( const T & value )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Appends value to the list.

See also append() and operator<<().

### QLinkedList & QLinkedList::operator<< ( const T & value )

Appends value to the list and returns a reference to this list.

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

### QLinkedList<T> & QLinkedList::operator= ( const QLinkedList & other )

Assigns other to this list and returns a reference to this list.

### bool QLinkedList::operator== ( const QLinkedList & other ) const

Returns true if other is equal to this list; otherwise returns false.

Two lists are considered equal if they contain the same values in the same order.

This function requires the value type to implement `operator==()`.

See also operator!=().

## Related Non-Members

### QDataStream & operator<< ( QDataStream & out, const QLinkedList<T> & list )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes the linked list list to stream out.

This function requires the value type to implement `operator<<()`.

See also Format of the QDataStream operators.

### QDataStream & operator>> ( QDataStream & in, QLinkedList<T> & list )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Reads a linked list from stream in into list.

This function requires the value type to implement `operator>>()`.

See also Format of the QDataStream operators.