Qt 4.8: iterator Class Reference

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# iterator Class Reference

(QSet::iterator)

The QSet::iterator class provides an STL-style non-const iterator for QSet. More...

     #include <QSet>

This class was introduced in Qt 4.2.

- List of all members, including inherited members

## Public Types

typedef | iterator_category

## Public Functions

| iterator ()
| iterator ( const iterator & other )
bool | operator!= ( const iterator & other ) const
bool | operator!= ( const const_iterator & other ) const
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 )
const T * | operator-> () const
iterator & | operator= ( const iterator & other )
bool | operator== ( const iterator & other ) const
bool | operator== ( const const_iterator & other ) const

## Detailed Description

The QSet::iterator class provides an STL-style non-const iterator for QSet.

QSet features both STL-style iterators and Java-style iterators. 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<T>::iterator allows you to iterate over a QSet and to remove items (using QSet::erase()) while you iterate. (QSet doesn't let you modify a value through an iterator, because that would potentially require moving the value in the internal hash table used by QSet.) If you want to iterate over a const QSet, you should use QSet::const_iterator. 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.

QSet<T>::iterator allows you to iterate over a QSet<T> and modify it as you go (using QSet::erase()). However,

The default QSet::iterator constructor creates an uninitialized iterator. You must initialize it using a function like QSet::begin(), QSet::end(), or 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>::iterator i;
     for (i = set.begin(); i != set.end(); ++i)
         qDebug() << *i;

Here's a loop that removes certain items (all those that start with 'J') from a set while iterating:

     QSet<QString> set;
     set << "January" << "February" << ... << "December";

     QSet<QString>::iterator i = set.begin();
     while (i != set.end()) {
         if ((*i).startsWith('J')) {
             i = set.erase(i);
         } else {
             ++i;
         }
     }

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

     QSet<QString> set;
     ...
     QSet<QString>::iterator it = qFind(set.begin(), set.end(), "Jeanette");
     if (it != set.end())
         cout << "Found Jeanette" << endl;

Multiple iterators can be used on the same set. However, you may not attempt to modify the container while iterating on it.

See also QSet::const_iterator and QMutableSetIterator.

## Member Type Documentation

### typedef iterator::iterator_category

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

## Member Function Documentation

### 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.

See also QSet::begin() and QSet::end().

### iterator::iterator ( const iterator & other )

Constructs a copy of other.

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

Returns true if other points to a different item than this iterator; otherwise returns false.

See also operator==().

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

This is an overloaded function.

### const T & iterator::operator* () const

Returns a reference to the current item.

See also operator->().

### iterator iterator::operator+ ( int j ) const

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 values.

See also operator-().

### iterator & 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::constEnd() leads to undefined results.

See also operator--().

### iterator iterator::operator++ ( int )

This is an overloaded function.

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

### iterator & iterator::operator+= ( int j )

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

This operation can be slow for large j values.

See also operator-=() and operator+().

### iterator iterator::operator- ( int j ) const

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 values.

See also operator+().

### 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 QSet::begin() leads to undefined results.

See also operator++().

### iterator iterator::operator-- ( int )

This is an overloaded function.

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

### iterator & iterator::operator-= ( int j )

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

This operation can be slow for large j values.

See also operator+=() and operator-().

### const T * iterator::operator-> () const

Returns a pointer to the current item.

See also operator*().

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

Assigns other to this iterator.

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

Returns true if other points to the same item as this iterator; otherwise returns false.

See also operator!=().

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

This is an overloaded function.