- Qt 5.15
- Qt Core
- C++ Classes
- const_iterator
- Qt 5.15.19 Reference Documentation

# const_iterator Class

class QFuture::const_iterator

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

This class was introduced in Qt 4.4.

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Types

typedef | difference_type
typedef | iterator_category
typedef | pointer
typedef | reference
typedef | value_type

## Public Functions

| 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+(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
bool | operator==(const const_iterator &other) const

## Detailed Description

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 << Qt::endl;

See also QFutureIterator and QFuture.

## 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(const const_iterator &other)

Constructs a copy of other.

### 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::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 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<T>::constEnd() leads to undefined results.

See also operator--().

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

This is an overloaded function.

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<T>::constBegin() leads to undefined results.

See also operator++().

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

This is an overloaded function.

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.

### 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!=().