const_iterator 类

class QSet ::const_iterator

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

该类在 Qt 4.2 引入。

公共类型

typedef	difference_type
typedef	iterator_category
typedef	pointer
typedef	reference
typedef	value_type

公共函数

	const_iterator (const iterator & other )
	const_iterator (const const_iterator & other )
	const_iterator ()
const_iterator &	operator= (const const_iterator & other )
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

QSet 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.

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

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

QSet<QString> set;
set << "January" << "February" << ... << "December";
QSet<QString>::const_iterator i;
for (i = set.begin(); i != set.end(); ++i)
    qDebug() << *i;

STL-style iterators can be used as arguments to 一般算法 . For example, here's how to find an item in the set using the qFind() algorithm:

QSet<QString> set;
...
const auto predicate = [](const QString &s) { return s.compare("Jeanette", Qt::CaseInsensitive) == 0; };
QSet<QString>::const_iterator it = std::find_if(set.cbegin(), set.cend(), predicate);
if (it != set.constEnd())
    cout << "Found Jeanette" << endl;

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 QSet::iterator and QSetIterator .

成员类型文档编制

typedef const_iterator:: iterator_category

Synonyms for std::bidirectional_iterator_tag indicating these iterators are bidirectional iterators.

成员函数文档编制

const_iterator const_iterator:: operator++ ( int )

这是重载函数。

The postfix ++ operator ( it++ ) advances the iterator to the next item in the set and returns an iterator to the previously current item.

const_iterator &const_iterator:: operator++ ()

The prefix ++ operator ( ++it ) advances the iterator to the next item in the set and returns an iterator to the new current item.

Calling this function on QSet <T>::constEnd() leads to undefined results.

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== ().

bool const_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!= ().

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

Returns a pointer to the current item.

另请参阅 operator* ().

const T &const_iterator:: operator* () const

Returns a reference to the current item.

另请参阅 operator-> ().

const_iterator &const_iterator:: operator= (const const_iterator & other )

赋值 other to this iterator.

const_iterator:: const_iterator (const const_iterator & other )

构造副本为 other .

const_iterator:: const_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 QSet::begin () 和 QSet::end ().

const_iterator:: const_iterator (const iterator & other )

这是重载函数。

构造副本为 other .

该函数在 Qt 4.2 引入。