iterator 类

( QList::iterator )

The QList::iterator 类提供 STL 样式非常量迭代器为 QList and QQueue . 更多...

头: #include <iterator>
qmake: QT += core

公共类型

typedef iterator_category

公共函数

iterator ()
iterator (const iterator & other )
bool operator!= (const iterator & other ) const
bool operator!= (const const_iterator & other ) const
T & operator* () const
iterator operator+ (iterator::difference_type j ) const
iterator & operator++ ()
iterator operator++ ( int )
iterator & operator+= (iterator::difference_type j )
iterator operator- (iterator::difference_type j ) const
int operator- (iterator other ) const
iterator & operator-- ()
iterator operator-- ( int )
iterator & operator-= (iterator::difference_type j )
T * operator-> () const
bool operator< (const iterator & other ) const
bool operator< (const const_iterator & other ) const
bool operator<= (const iterator & other ) const
bool operator<= (const const_iterator & other ) const
bool operator== (const iterator & other ) const
bool operator== (const const_iterator & other ) const
bool operator> (const iterator & other ) const
bool operator> (const const_iterator & other ) const
bool operator>= (const iterator & other ) const
bool operator>= (const const_iterator & other ) const
T & operator[] (iterator::difference_type j ) const

公共变量

QList::Node * i

详细描述

The QList::iterator 类提供 STL 样式非常量迭代器为 QList and QQueue .

QList 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.

QList <T>::iterator allows you to iterate over a QList <T> (or QQueue <T>) and to modify the list item associated with the iterator. If you want to iterate over a const QList ,使用 QList::const_iterator instead. It is generally good practice to use QList::const_iterator on a non-const QList as well, unless you need to change the QList through the iterator. Const iterators are slightly faster, and can improve code readability.

默认 QList::iterator constructor creates an uninitialized iterator. You must initialize it using a QList function like QList::begin (), QList::end (),或 QList::insert () before you can start iterating. Here's a typical loop that prints all the items stored in a list:

QList<QString> list;
list.append("January");
list.append("February");
...
list.append("December");
QList<QString>::iterator i;
for (i = list.begin(); i != list.end(); ++i)
    cout << *i << endl;
					

Let's see a few examples of things we can do with a QList::iterator that we cannot do with a QList::const_iterator . Here's an example that increments every value stored in a QList <int> by 2:

QList<int>::iterator i;
for (i = list.begin(); i != list.end(); ++i)
    *i += 2;
					

Most QList functions accept an integer index rather than an iterator. For that reason, iterators are rarely useful in connection with QList . One place where STL-style iterators do make sense is as arguments to 一般算法 .

For example, here's how to delete all the widgets stored in a QList < QWidget *>:

QList<QWidget *> list;
...
qDeleteAll(list.begin(), list.end());
					

Multiple iterators can be used on the same list. However, be aware that any non-const function call performed on the QList will render all existing iterators undefined. If you need to keep iterators over a long period of time, we recommend that you use QLinkedList 而不是 QList .

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 QList::const_iterator and QMutableListIterator .

成员类型文档编制

typedef iterator:: iterator_category

同义词 std::random_access_iterator_tag indicating this iterator is a random access iterator.

成员函数文档编制

bool iterator:: operator>= (const iterator & other ) const

bool iterator:: operator>= (const const_iterator & other ) const

返回 true if the item pointed to by this iterator is greater than or equal to the item pointed to by the other iterator.

bool iterator:: operator> (const iterator & other ) const

bool iterator:: operator> (const const_iterator & other ) const

返回 true if the item pointed to by this iterator is greater than the item pointed to by the other iterator.

bool iterator:: operator<= (const iterator & other ) const

bool iterator:: operator<= (const const_iterator & other ) const

返回 true if the item pointed to by this iterator is less than or equal to the item pointed to by the other iterator.

bool iterator:: operator< (const iterator & other ) const

bool iterator:: operator< (const const_iterator & other ) const

返回 true if the item pointed to by this iterator is less than the item pointed to by the other iterator.

bool iterator:: operator!= (const iterator & other ) const

bool 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== ().

bool iterator:: operator== (const iterator & other ) const

bool iterator:: operator== (const 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!= ().

iterator:: iterator ()

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 QList::begin () 和 QList::end ().

iterator:: iterator (const iterator & other )

构造副本为 other .

T &iterator:: operator* () const

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-> ().

iterator iterator:: operator+ ( iterator::difference_type j ) const

Returns an iterator to the item at j positions forward from this iterator. (If j is negative, the iterator goes backward.)

另请参阅 operator- () 和 operator+= ().

iterator &iterator:: 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 QList::end () leads to undefined results.

另请参阅 operator-- ().

iterator iterator:: operator++ ( int )

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.

iterator &iterator:: operator+= ( iterator::difference_type j )

Advances the iterator by j items. (If j is negative, the iterator goes backward.)

另请参阅 operator-= () 和 operator+ ().

iterator iterator:: operator- ( iterator::difference_type j ) const

Returns an iterator to the item at j positions backward from this iterator. (If j is negative, the iterator goes forward.)

另请参阅 operator+ () 和 operator-= ().

int iterator:: operator- ( iterator other ) const

Returns the number of items between the item pointed to by other and the item pointed to by this iterator.

iterator &iterator:: operator-- ()

The prefix -- operator ( --it ) makes the preceding item current and returns an iterator to the new current item.

Calling this function on QList::begin () leads to undefined results.

另请参阅 operator++ ().

iterator iterator:: operator-- ( int )

这是重载函数。

The postfix -- operator ( it-- ) makes the preceding item current and returns an iterator to the previously current item.

iterator &iterator:: operator-= ( iterator::difference_type j )

Makes the iterator go back by j items. (If j is negative, the iterator goes forward.)

另请参阅 operator+= () 和 operator- ().

T *iterator:: operator-> () const

Returns a pointer to the current item.

另请参阅 operator* ().

T &iterator:: operator[] ( iterator::difference_type j ) const

Returns a modifiable reference to the item at position *this + j .

This function is provided to make QList iterators behave like C++ pointers.

另请参阅 operator+ ().