const_iterator 类

class QMultiHash ::const_iterator

The QMultiHash::const_iterator 类提供 STL 样式 const 迭代器为 QMultiHash . 更多...

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公共函数

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

详细描述

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

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

QHash<QString, int> hash;
hash.insert("January", 1);
hash.insert("February", 2);
...
hash.insert("December", 12);
for (auto i = hash.cbegin(), end = hash.cend(); i != end; ++i)
    cout << qPrintable(i.key()) << ": " << i.value() << endl;
					

不像 QMap , which orders its items by key, QMultiHash stores its items in an arbitrary order. The only guarantee is that items that share the same key (because they were inserted using a QMultiHash ) will appear consecutively, from the most recently to the least recently inserted value.

Multiple iterators can be used on the same hash. However, be aware that any modification performed directly on the QMultiHash (inserting and removing items) can cause the iterators to become invalid.

Inserting items into the hash or calling methods such as QMultiHash::reserve() or QMultiHash::squeeze() can invalidate all iterators pointing into the hash. Iterators are guaranteed to stay valid only as long as the QMultiHash doesn't have to grow/shrink it's internal hash table. Using any iterator after a rehashing operation ahs occurred will lead to undefined behavior.

If you need to keep iterators over a long period of time, we recommend that you use QMultiMap 而不是 QMultiHash .

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 QMultiHash::iterator , QMultiHash::key_iterator ，和 QMultiHash::const_key_value_iterator .

成员函数文档编制

[constexpr noexcept] 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 QMultiHash::constBegin () 和 QMultiHash::constEnd ().

[noexcept] const_iterator:: const_iterator (const QMultiHash < Key , T > ::iterator & other )

构造副本为 other .

[noexcept] const Key &const_iterator:: key () const

Returns the current item's key.

另请参阅 value ().

[noexcept] T &const_iterator:: value () const

Returns the current item's value.

另请参阅 key () 和 operator* ().

[noexcept] bool const_iterator:: operator!= (const QMultiHash < Key , T > ::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== ().

[noexcept] T &const_iterator:: operator* () const

Returns the current item's value.

如同 value ().

另请参阅 key ().

[noexcept] QMultiHash < Key , T > ::const_iterator &const_iterator:: operator++ ()

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

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

[noexcept] QMultiHash < Key , T > ::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 hash and returns an iterator to the previously current item.

[noexcept] T *const_iterator:: operator-> () const

Returns a pointer to the current item's value.

另请参阅 value ().

[noexcept] bool const_iterator:: operator== (const QMultiHash < Key , T > ::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!= ().

内容

• 公共函数

• 详细描述