const_iterator 类

class QMap ::const_iterator

The QMap::const_iterator 类提供 STL 样式 const 迭代器为 QMap and QMultiMap . 更多...

所有成员列表，包括继承成员

公共类型

typedef

iterator_category

公共函数

	const_iterator (const iterator & other )
	const_iterator ()
const Key &	key () const
const T &	value () const
bool	operator!= (const const_iterator & other ) const
const T &	operator* () const
const_iterator	operator+ (int j ) const
const_iterator &	operator++ ()
const_iterator	operator++ ( int )
const_iterator &	operator+= (int j )
const_iterator	operator- (int j ) const
const_iterator &	operator-- ()
const_iterator	operator-- ( int )
const_iterator &	operator-= (int j )
const T *	operator-> () const
bool	operator== (const const_iterator & other ) const

详细描述

QMap features both STL 样式迭代器 and Java 风格迭代器 . 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.

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

默认 QMap::const_iterator constructor creates an uninitialized iterator. You must initialize it using a QMap function like QMap::constBegin (), QMap::constEnd ()，或 QMap::find () before you can start iterating. Here's a typical loop that prints all the (key, value) pairs stored in a map:

QMap<QString, int> map;
map.insert("January", 1);
map.insert("February", 2);
...
map.insert("December", 12);
QMap<QString, int>::const_iterator i;
for (i = map.constBegin(); i != map.constEnd(); ++i)
    cout << i.key() << ": " << i.value() << Qt::endl;

不像 QHash , which stores its items in an arbitrary order, QMap stores its items ordered by key. Items that share the same key (because the map is a QMultiMap ) will appear consecutively, from the most recently to the least recently inserted value.

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

警告： 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 隐式共享迭代器问题 .

另请参阅 QMap::iterator , QMap::key_iterator ，和 QMapIterator .

成员类型文档编制

typedef const_iterator:: iterator_category

同义词 std::bidirectional_iterator_tag indicating this iterator is a bidirectional iterator.

成员函数文档编制

const_iterator:: const_iterator (const iterator & other )

构造副本为 other .

const_iterator:: const_iterator ()

Constructs an uninitialized iterator.

Functions like key (), value (), and operator++() must not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.

另请参阅 QMap::constBegin () 和 QMap::constEnd ().

const Key &const_iterator:: key () const

Returns the current item's key.

另请参阅 value ().

const T &const_iterator:: value () const

Returns the current item's value.

另请参阅 key () 和 operator* ().

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

返回 true if other 指向与此迭代器不同的项；否则返回 false .

另请参阅 operator== ().

const T &const_iterator:: operator* () const

Returns the current item's value.

如同 value ().

另请参阅 key ().

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 值。

另请参阅 operator- ().

const_iterator &const_iterator:: operator++ ()

The prefix ++ operator ( ++i ) advances the iterator to the next item in the map and returns an iterator to the new current item.

Calling this function on QMap::end () leads to undefined results.

另请参阅 operator-- ().

const_iterator const_iterator:: operator++ ( int )

这是重载函数。

The postfix ++ operator ( i++ ) advances the iterator to the next item in the map 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.)

This operation can be slow for large j 值。

另请参阅 operator-= () 和 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.)

This operation can be slow for large j 值。

另请参阅 operator+ ().

const_iterator &const_iterator:: operator-- ()

The prefix -- operator ( --i ) makes the preceding item current and returns an iterator pointing to the new current item.

Calling this function on QMap::begin () leads to undefined results.

另请参阅 operator++ ().

const_iterator const_iterator:: operator-- ( int )

这是重载函数。

The postfix -- operator ( i-- ) makes the preceding item current and returns an iterator pointing 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.)

This operation can be slow for large j 值。

另请参阅 operator+= () 和 operator- ().

const T *const_iterator:: operator-> () const

Returns a pointer to the current item's value.

另请参阅 value ().

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

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

另请参阅 operator!= ().