The QHash::const_iterator 類提供 STL 樣式 const 迭代器為 QHash and QMultiHash . 更多...
| 頭： | #include <const_iterator> |
| qmake: | QT += core |
| 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+ (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 |
The QHash::const_iterator 類提供 STL 樣式 const 迭代器為 QHash and QMultiHash .
QHash features both STL 樣式迭代器 and Java 風格迭代器 . 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.
QHash <Key, T>::const_iterator allows you to iterate over a QHash (or a QMultiHash ). 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.
默認 QHash::const_iterator constructor creates an uninitialized iterator. You must initialize it using a QHash function like QHash::constBegin (), QHash::constEnd ()，或 QHash::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() << 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 QHash::insertMulti ()) 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 has the potential of dramatically changing the order in which the items are stored in the hash, as they might cause QHash to rehash its internal data structure. 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 隱式共享迭代器問題 .
另請參閱 QHash::iterator and QHashIterator .
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 QHash::constBegin () 和 QHash::constEnd ().
構造副本為 other .
Returns the current item's key.
另請參閱 value ().
Returns the current item's value.
返迴
true
if
other
指嚮與此迭代器不同的項；否則返迴
false
.
另請參閱 operator== ().
Returns the current item's value.
如同 value ().
另請參閱 key ().
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。
另請參閱 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.
另請參閱 operator-- ().
這是重載函數。
The postfix ++ operator (
i++
) advances the iterator to the next item in the hash and returns an iterator to the previously current item.
推進迭代器 j items. (If j is negative, the iterator goes backward.)
This operation can be slow for large j 值。
另請參閱 operator-= () 和 operator+ ().
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。
另請參閱 operator+ ().
The prefix -- operator (
--i
) makes the preceding item current and returns an iterator pointing to the new current item.
Calling this function on QHash::begin () leads to undefined results.
另請參閱 operator++ ().
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.
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。
另請參閱 operator+= () 和 operator- ().
Returns a pointer to the current item's value.
另請參閱 value ().
返迴
true
if
other
points to the same item as this iterator; otherwise returns
false
.
另請參閱 operator!= ().
