Qt 4.8: QFutureIterator Class Reference

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# QFutureIterator Class Reference

The QFutureIterator class provides a Java-style const iterator for QFuture. More...

     #include <QFutureIterator>

Note: All functions in this class are reentrant.

This class was introduced in Qt 4.4.

- List of all members, including inherited members

## Public Functions

| QFutureIterator ( const QFuture<T> & future )
bool | findNext ( const T & value )
bool | findPrevious ( const T & value )
bool | hasNext () const
bool | hasPrevious () const
const T & | next ()
const T & | peekNext () const
const T & | peekPrevious () const
const T & | previous ()
void | toBack ()
void | toFront ()
QFutureIterator & | operator= ( const QFuture<T> & future )

## Detailed Description

The QFutureIterator class provides a Java-style const iterator for QFuture.

QFuture has both Java-style iterators and STL-style iterators. The Java-style iterators are more high-level and easier to use than the STL-style iterators; on the other hand, they are slightly less efficient.

An alternative to using iterators is to use index positions. Some QFuture member functions take an index as their first parameter, making it possible to access results without using iterators.

QFutureIterator<T> allows you to iterate over a QFuture<T>. Note that there is no mutable iterator for QFuture (unlike the other Java-style iterators).

The QFutureIterator constructor takes a QFuture as its argument. After construction, the iterator is located at the very beginning of the result list (i.e. before the first result). Here's how to iterate over all the results sequentially:

     QFuture<QString> future;
     ...
     QFutureIterator<QString> i(future);
     while (i.hasNext())
         qDebug() << i.next();

The next() function returns the next result (waiting for it to become available, if necessary) from the future and advances the iterator. Unlike STL-style iterators, Java-style iterators point between results rather than directly at results. The first call to next() advances the iterator to the position between the first and second result, and returns the first result; the second call to next() advances the iterator to the position between the second and third result, and returns the second result; and so on.

Here's how to iterate over the elements in reverse order:

     QFutureIterator<QString> i(future);
     i.toBack();
     while (i.hasPrevious())
         qDebug() << i.previous();

If you want to find all occurrences of a particular value, use findNext() or findPrevious() in a loop.

Multiple iterators can be used on the same future. If the future is modified while a QFutureIterator is active, the QFutureIterator will continue iterating over the original future, ignoring the modified copy.

See also QFuture::const_iterator and QFuture.

## Member Function Documentation

### QFutureIterator::QFutureIterator ( const QFuture<T> & future )

Constructs an iterator for traversing future. The iterator is set to be at the front of the result list (before the first result).

See also operator=().

### bool QFutureIterator::findNext ( const T & value )

Searches for value starting from the current iterator position forward. Returns true if value is found; otherwise returns false.

After the call, if value was found, the iterator is positioned just after the matching result; otherwise, the iterator is positioned at the back of the result list.

See also findPrevious().

### bool QFutureIterator::findPrevious ( const T & value )

Searches for value starting from the current iterator position backward. Returns true if value is found; otherwise returns false.

After the call, if value was found, the iterator is positioned just before the matching result; otherwise, the iterator is positioned at the front of the result list.

See also findNext().

### bool QFutureIterator::hasNext () const

Returns true if there is at least one result ahead of the iterator, e.g., the iterator is not at the back of the result list; otherwise returns false.

See also hasPrevious() and next().

### bool QFutureIterator::hasPrevious () const

Returns true if there is at least one result ahead of the iterator, e.g., the iterator is not at the front of the result list; otherwise returns false.

See also hasNext() and previous().

### const T & QFutureIterator::next ()

Returns the next result and advances the iterator by one position.

Calling this function on an iterator located at the back of the result list leads to undefined results.

See also hasNext(), peekNext(), and previous().

### const T & QFutureIterator::peekNext () const

Returns the next result without moving the iterator.

Calling this function on an iterator located at the back of the result list leads to undefined results.

See also hasNext(), next(), and peekPrevious().

### const T & QFutureIterator::peekPrevious () const

Returns the previous result without moving the iterator.

Calling this function on an iterator located at the front of the result list leads to undefined results.

See also hasPrevious(), previous(), and peekNext().

### const T & QFutureIterator::previous ()

Returns the previous result and moves the iterator back by one position.

Calling this function on an iterator located at the front of the result list leads to undefined results.

See also hasPrevious(), peekPrevious(), and next().

### void QFutureIterator::toBack ()

Moves the iterator to the back of the result list (after the last result).

See also toFront() and previous().

### void QFutureIterator::toFront ()

Moves the iterator to the front of the result list (before the first result).

See also toBack() and next().

### QFutureIterator & QFutureIterator::operator= ( const QFuture<T> & future )

Makes the iterator operate on future. The iterator is set to be at the front of the result list (before the first result).

See also toFront() and toBack().