iterator 類

class QMap ::iterator

The QMap::iterator 類提供 STL 樣式非常量迭代器為 QMap . 更多...

• 所有成員列錶，包括繼承成員
• Deprecated members

公共類型

iterator_category

公共函數

	iterator ()
const Key &	key () const
T &	value () const
T &	operator* () const
iterator &	operator++ ()
iterator	operator++ (int)
iterator &	operator-- ()
iterator	operator-- (int)
T *	operator-> () const

相關非成員

bool	operator!= (const iterator & lhs , const iterator & rhs )
bool	operator== (const iterator & lhs , const iterator & rhs )

詳細描述

QMap <Key, T>::iterator allows you to iterate over a QMap and to modify the value (but not the key) stored under a particular key. If you want to iterate over a const QMap , you should use QMap::const_iterator . 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.

默認 QMap::iterator constructor creates an uninitialized iterator. You must initialize it using a QMap function like QMap::begin (), QMap::end ()，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);
for (auto i = map.cbegin(), end = map.cend(); i != end; ++i)
    cout << qPrintable(i.key()) << ": " << i.value() << endl;
					

不像 QHash , which stores its items in an arbitrary order, QMap stores its items ordered by key.

Here's an example that increments every value stored in the QMap by 2:

for (auto i = map.begin(), end = map.end(); i != end; ++i)
    i.value() += 2;
					

To remove elements from a QMap you can use erase_if ( QMap <Key, T> &map, Predicate pred):

erase_if(map, [](const QMap<QString, int>::iterator it) { return it.value() > 10; });
					

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 隱式共享迭代器問題 .

另請參閱 QMap::const_iterator , QMap::key_iterator ，和 QMap::key_value_iterator .

成員類型文檔編製

[alias] iterator:: iterator_category

同義詞 std::bidirectional_iterator_tag indicating this iterator is a bidirectional iterator.

成員函數文檔編製

iterator:: 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.

另請參閱 QMap::begin () 和 QMap::end ().

const Key &iterator:: key () const

Returns the current item's key as a const reference.

There is no direct way of changing an item's key through an iterator, although it can be done by calling QMap::erase () followed by QMap::insert ().

另請參閱 value ().

T &iterator:: value () const

Returns a modifiable reference to the current item's value.

You can change the value of an item by using value() on the left side of an assignment, for example:

if (i.key() == "Hello")
    i.value() = "Bonjour";
					

另請參閱 key () 和 operator* ().

T &iterator:: operator* () const

Returns a modifiable reference to the current item's value.

如同 value ().

另請參閱 key ().

iterator &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.

另請參閱 operator-- ().

iterator iterator:: operator++ ( int )

這是重載函數。

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

iterator &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.

另請參閱 operator++ ().

iterator iterator:: operator-- ( int )

這是重載函數。

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

T *iterator:: operator-> () const

Returns a pointer to the current item's value.

另請參閱 value ().

相關非成員

bool operator== (const iterator & lhs , const iterator & rhs )

返迴 true if lhs points to the same item as the rhs iterator; otherwise returns false .

另請參閱 operator!= ().

bool operator!= (const iterator & lhs , const iterator & rhs )

返迴 true if lhs points to a different item than the rhs iterator; otherwise returns false .

另請參閱 operator== ().

內容

1. 公共類型

2. 公共函數

3. 相關非成員

4. 詳細描述