The QLinkedList::iterator 类提供 STL 样式非常量迭代器为 QLinkedList . 更多...
| iterator () | |
| bool | operator!= (const iterator & other ) const |
| bool | operator!= (const const_iterator & other ) const |
| T & | operator* () const |
| iterator | operator+ (int j ) const |
| iterator & | operator++ () |
| iterator | operator++ (int) |
| iterator & | operator+= (int j ) |
| iterator | operator- (int j ) const |
| iterator & | operator-- () |
| iterator | operator-- (int) |
| iterator & | operator-= (int j ) |
| T * | operator-> () const |
| bool | operator== (const iterator & other ) const |
| bool | operator== (const const_iterator & other ) const |
QLinkedList 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.
QLinkedList <T>::iterator allows you to iterate over a QLinkedList <T> and to modify the list item associated with the iterator. If you want to iterate over a const QLinkedList ，使用 QLinkedList::const_iterator instead. It is generally good practice to use QLinkedList::const_iterator on a non-const QLinkedList as well, unless you need to change the QLinkedList through the iterator. Const iterators are slightly faster, and can improve code readability.
默认 QLinkedList::iterator constructor creates an uninitialized iterator. You must initialize it using a function like QLinkedList::begin (), QLinkedList::end ()，或 QLinkedList::insert () before you can start iterating. Here's a typical loop that prints all the items stored in a list:
QLinkedList<QString> list; list.append("January"); list.append("February"); ... list.append("December"); QLinkedList<QString>::iterator i; for (i = list.begin(); i != list.end(); ++i) cout << *i << Qt::endl;
STL-style iterators can be used as arguments to 一般算法 . For example, here's how to find an item in the list:
QLinkedList<QString> list; ... QLinkedList<QString>::iterator it = std::find(list.begin(), list.end(), "Joel"); if (it != list.end()) cout << "Found Joel" << Qt::endl;
Let's see a few examples of things we can do with a QLinkedList::iterator that we cannot do with a QLinkedList::const_iterator . Here's an example that increments every value stored in a QLinkedList <int> by 2:
QLinkedList<int>::iterator i; for (i = list.begin(); i != list.end(); ++i) *i += 2;
Here's an example that removes all the items that start with an underscore character in a QLinkedList < QString >:
QLinkedList<QString> list; ... QLinkedList<QString>::iterator i = list.begin(); while (i != list.end()) { if ((*i).startsWith('_')) i = list.erase(i); else ++i; }
The call to QLinkedList::erase () removes the item pointed to by the iterator from the list, and returns an iterator to the next item. Here's another way of removing an item while iterating:
QLinkedList<QString>::iterator i = list.begin(); while (i != list.end()) { QLinkedList<QString>::iterator previous = i; ++i; if ((*previous).startsWith('_')) list.erase(previous); }
It might be tempting to write code like this:
// WRONG while (i != list.end()) { if ((*i).startsWith('_')) list.erase(i); ++i; }
However, this will potentially crash in
++i
，因为
i
is a dangling iterator after the call to
erase
().
Multiple iterators can be used on the same list. If you add items to the list, existing iterators will remain valid. If you remove items from the list, 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 隐式共享迭代器问题 .
另请参阅 QLinkedList::const_iterator and QMutableLinkedListIterator .
返回
true
if
other
points to the same item as this iterator; otherwise returns
false
.
另请参阅 operator!= ().
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== ().
Constructs an uninitialized iterator.
Functions like operator*() and operator++() should not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.
另请参阅 QLinkedList::begin () 和 QLinkedList::end ().
Returns a modifiable reference to the current item.
You can change the value of an item by using operator*() on the left side of an assignment, for example:
if (*it == "Hello") *it = "Bonjour";
另请参阅 operator-> ().
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。
另请参阅 operator- ().
The prefix ++ operator (
++it
) advances the iterator to the next item in the list and returns an iterator to the new current item.
Calling this function on QLinkedList::end () leads to undefined results.
另请参阅 operator-- ().
这是重载函数。
The postfix ++ operator (
it++
) advances the iterator to the next item in the list and returns an iterator to the previously current item.
Advances the iterator by j items. (If j is negative, the iterator goes backward.)
另请参阅 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。
另请参阅 operator+ ().
The prefix – operator (
--it
) makes the preceding item current and returns an iterator to the new current item.
Calling this function on QLinkedList::begin () leads to undefined results.
另请参阅 operator++ ().
这是重载函数。
The postfix – operator (
it--
) makes the preceding item current and returns an iterator to the previously current item.
Makes the iterator go back by j items. (If j is negative, the iterator goes forward.)
另请参阅 operator+= () 和 operator- ().
Returns a pointer to the current item.
另请参阅 operator* ().
