const_iterator 类

class QHash ::const_iterator

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

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公共函数

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

详细描述

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

默认 QHash::const_iterator constructor creates an uninitialized iterator. You must initialize it using a QHash function like QHash::cbegin (), QHash::cend ()，或 QHash::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, QHash 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 QHash (inserting and removing items) can cause the iterators to become invalid.

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

You can however safely use iterators to remove entries from the hash using the QHash::erase () method. This function can safely be called while iterating, and won't affect the order of items in the hash.

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 QHash::iterator , QHash::key_iterator ，和 QHash::const_key_value_iterator .

成员函数文档编制

`[constexpr]` 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 QHash::constBegin () 和 QHash::constEnd ().

const_iterator:: const_iterator (const iterator & other )

构造副本为 other .

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++ ()

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 QHash::end () leads to undefined results.

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.

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

Returns a pointer to the current item's value.