Contents

• Public Types
• Public Functions
• Detailed Description

Detailed Description

TheQList::const_iterator class provides an STL-style const iterator forQList andQQueue.

QList provides bothSTL-style iterators andJava-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 aQList<T> (or aQQueue<T>). If you want to modify theQList as you iterate over it, useQList::iterator instead. It is generally good practice to useQList::const_iterator on a non-constQList as well, unless you need to change theQList through the iterator. Const iterators are slightly faster, and can improve code readability.

The defaultQList::const_iterator constructor creates an uninitialized iterator. You must initialize it using aQList function likeQList::constBegin(),QList::constEnd(), orQList::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;

MostQList functions accept an integer index rather than an iterator. For that reason, iterators are rarely useful in connection withQList. One place where STL-style iterators do make sense is as arguments togeneric algorithms.

For example, here's how to delete all the widgets stored in aQList<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 theQList will render all existing iterators undefined. If you need to keep iterators over a long period of time, we recommend that you useQLinkedList rather thanQList.

Member Type Documentation

typedef const_iterator::iterator_category

A synonym forstd::random_access_iterator_tag indicating this iterator is a random access iterator.

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 alsoQList::constBegin() andQList::constEnd().

const_iterator::const_iterator(constconst_iterator & other)

Constructs a copy ofother.

const_iterator::const_iterator(constiterator & other)

Constructs a copy ofother.

bool const_iterator::operator!=(constconst_iterator & other) const

Returns true ifother points to a different item than this iterator; otherwise returns false.

See alsooperator==().

constT & const_iterator::operator*() const

Returns the current item.

See alsooperator->().

const_iterator const_iterator::operator+(int j) const

Returns an iterator to the item atj positions forward from this iterator. (Ifj is negative, the iterator goes backward.)

See alsooperator-() andoperator+=().

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 onQList::end() leads to undefined results.

See alsooperator--().

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 byj items. (Ifj is negative, the iterator goes backward.)

See alsooperator-=() andoperator+().

const_iterator const_iterator::operator-(int j) const

Returns an iterator to the item atj positions backward from this iterator. (Ifj is negative, the iterator goes forward.)

See alsooperator+() andoperator-=().

int const_iterator::operator-(const_iterator other) const

Returns the number of items between the item pointed to byother 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 onQList::begin() leads to undefined results.

See alsooperator++().

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 byj items. (Ifj is negative, the iterator goes forward.)

See alsooperator+=() andoperator-().

constT * const_iterator::operator->() const

Returns a pointer to the current item.

See alsooperator*().

bool const_iterator::operator<(constconst_iterator & other) const

Returns true if the item pointed to by this iterator is less than the item pointed to by theother iterator.

bool const_iterator::operator<=(constconst_iterator & other) const

Returns true if the item pointed to by this iterator is less than or equal to the item pointed to by theother iterator.

bool const_iterator::operator==(constconst_iterator & other) const

Returns true ifother points to the same item as this iterator; otherwise returns false.

See alsooperator!=().

bool const_iterator::operator>(constconst_iterator & other) const

Returns true if the item pointed to by this iterator is greater than the item pointed to by theother iterator.

bool const_iterator::operator>=(constconst_iterator & other) const

Returns true if the item pointed to by this iterator is greater than or equal to the item pointed to by theother iterator.

constT & const_iterator::operator[](int j) const

Returns the item at position *this +j.

This function is provided to makeQList iterators behave like C++ pointers.

See alsooperator+().