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# const_iterator Class Reference
(QFuture::const_iterator)
[QtCore module]

The QFuture::const_iterator class provides an STL-style const iterator for QFuture. More...

     #include <QFuture>

Warning: All the functions in this class are reentrant.

This class was introduced in Qt 4.4.

- List of all members, including inherited members

### Public Types

- typedef difference_type
- typedef iterator_category
- typedef pointer
- typedef reference
- typedef value_type

### Public Functions

- const_iterator ()
- const_iterator ( const const_iterator & other )
- 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
- const_iterator & operator= ( const const_iterator & other )
- bool operator== ( const const_iterator & other ) const

## Detailed Description

The QFuture::const_iterator class provides an STL-style const iterator for QFuture.

QFuture provides 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.

The default QFuture::const_iterator constructor creates an uninitialized iterator. You must initialize it using a QFuture function like QFuture::constBegin() or QFuture::constEnd() before you start iterating. Here's a typical loop that prints all the results available in a future:

             QFuture<QString> future = ...;

             QFuture<QString>::const_iterator i;
             for (i = future.constBegin(); i != future.constEnd(); ++i)
                 cout << *i << endl;

See also QFutureIterator.

## Member Type Documentation

### typedef const_iterator::difference_type

Typedef for ptrdiff_t. Provided for STL compatibility.

### typedef const_iterator::iterator_category

Typedef for std::bidirectional_iterator_tag. Provided for STL compatibility.

### typedef const_iterator::pointer

Typedef for const T *. Provided for STL compatibility.

### typedef const_iterator::reference

Typedef for const T &. Provided for STL compatibility.

### typedef const_iterator::value_type

Typedef for T. Provided for STL compatibility.

## Member Function Documentation

### const_iterator::const_iterator ()

Constructs an uninitialized iterator.

Functions like operator*() and operator++() should not be called on an uninitialized iterartor. Use operator=() to assign a value to it before using it.

See also QFuture::constBegin() and QFuture::constEnd().

### const_iterator::const_iterator ( const const_iterator & other )

Constructs a copy of other.

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

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

See also operator==().

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

Returns the current result.

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

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

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

### const_iterator & const_iterator::operator++ ()

The prefix ++ operator (`++it`) advances the iterator to the next result in the future and returns an iterator to the new current result.

Calling this function on QFuture::constEnd() leads to undefined results.

See also operator--().

### const_iterator const_iterator::operator++ ( int )

This is an overloaded member function, provided for convenience.

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

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

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

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

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

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

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

### const_iterator & const_iterator::operator-- ()

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

Calling this function on QFuture::constBegin() leads to undefined results.

See also operator++().

### const_iterator const_iterator::operator-- ( int )

This is an overloaded member function, provided for convenience.

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

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

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

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

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

Returns a pointer to the current result.

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

Assigns other to this iterator.

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

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

See also operator!=().