QMultiHash::const_iterator 类提供 STL 样式 const 迭代器为 QMultiHash . 更多...
| const_iterator (const iterator & other ) | |
| const_iterator () | |
| const Key & | key () const |
| T & | value () const |
| bool | operator!= (const const_iterator & other ) const |
| T & | operator* () const |
| const_iterator & | operator++ () |
| const_iterator | operator++ (int) |
| T * | operator-> () const |
| bool | operator== (const const_iterator & other ) const |
QMultiHash 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.
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::constBegin (), QMultiHash::constEnd ()，或 QMultiHash::find () 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); QHash<QString, int>::const_iterator i; for (i = hash.constBegin(); i != hash.constEnd(); ++i) cout << i.key() << ": " << i.value() << Qt::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 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 it's internal hash table. Using any iterator after a rehashing operation ahs 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.
If you need to keep iterators over a long period of time, we recommend that you use QMap 而不是 QHash .
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 .
构造副本为 other .
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 ().
Returns the current item's key.
另请参阅 value ().
Returns the current item's value.
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== ().
Returns the current item's value.
如同 value ().
另请参阅 key ().
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.
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.
Returns a pointer to the current item's value.
另请参阅 value ().
返回
true
if
other
points to the same item as this iterator; otherwise returns
false
.
另请参阅 operator!= ().
