Contents

• Public Functions
• Detailed Description

Detailed Description

TheQHashIterator class provides a Java-style const iterator forQHash andQMultiHash.

QHash has bothJava-style iterators andSTL-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.

QHashIterator<Key, T> allows you to iterate over aQHash (or aQMultiHash). If you want to modify the hash as you iterate over it, useQMutableHashIterator instead.

TheQHashIterator constructor takes aQHash as argument. After construction, the iterator is located at the very beginning of the hash (before the first item). Here's how to iterate over all the elements sequentially:

QHash<int,QWidget*> hash;...QHashIterator<int,QWidget*> i(hash);while (i.hasNext()) {    i.next();qDebug()<< i.key()<<": "<< i.value();}

Thenext() function returns the next item in the hash and advances the iterator. Thekey() andvalue() functions return the key and value of the last item that was jumped over.

Unlike STL-style iterators, Java-style iterators pointbetween items rather than directlyat items. The first call tonext() advances the iterator to the position between the first and second item, and returns the first item; the second call tonext() advances the iterator to the position between the second and third item; and so on.

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

QHashIterator<int,QWidget*> i(hash);i.toBack();while (i.hasPrevious()) {    i.previous();qDebug()<< i.key()<<": "<< i.value();}

If you want to find all occurrences of a particular value, usefindNext() orfindPrevious() in a loop. For example:

QHashIterator<int,QWidget*> i(hash);while (i.findNext(widget)) {qDebug()<<"Found widget "<< widget<<" under key "<< i.key();}

Multiple iterators can be used on the same hash. If the hash is modified while aQHashIterator is active, theQHashIterator will continue iterating over the original hash, ignoring the modified copy.

Member Function Documentation

QHashIterator::QHashIterator(constQHash<Key,T> & hash)

Constructs an iterator for traversinghash. The iterator is set to be at the front of the hash (before the first item).

See alsooperator=().

bool QHashIterator::findNext(constT & value)

Searches forvalue starting from the current iterator position forward. Returns true if a (key, value) pair with valuevalue is found; otherwise returns false.

After the call, ifvalue was found, the iterator is positioned just after the matching item; otherwise, the iterator is positioned at the back of the container.

See alsofindPrevious().

bool QHashIterator::findPrevious(constT & value)

Searches forvalue starting from the current iterator position backward. Returns true if a (key, value) pair with valuevalue is found; otherwise returns false.

After the call, ifvalue was found, the iterator is positioned just before the matching item; otherwise, the iterator is positioned at the front of the container.

See alsofindNext().

bool QHashIterator::hasNext() const

Returns true if there is at least one item ahead of the iterator, i.e. the iterator isnot at the back of the container; otherwise returns false.

See alsohasPrevious() andnext().

bool QHashIterator::hasPrevious() const

Returns true if there is at least one item behind the iterator, i.e. the iterator isnot at the front of the container; otherwise returns false.

See alsohasNext() andprevious().

constKey & QHashIterator::key() const

Returns the key of the last item that was jumped over using one of the traversal functions (next(),previous(),findNext(),findPrevious()).

After a call tonext() orfindNext(), key() is equivalent topeekPrevious().key(). After a call toprevious() orfindPrevious(), key() is equivalent topeekNext().key().

See alsovalue().

Item QHashIterator::next()

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

Callkey() on the return value to obtain the item's key, andvalue() to obtain the value.

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

See alsohasNext(),peekNext(), andprevious().

Item QHashIterator::peekNext() const

Returns the next item without moving the iterator.

Callkey() on the return value to obtain the item's key, andvalue() to obtain the value.

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

See alsohasNext(),next(), andpeekPrevious().

Item QHashIterator::peekPrevious() const

Returns the previous item without moving the iterator.

Callkey() on the return value to obtain the item's key, andvalue() to obtain the value.

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

See alsohasPrevious(),previous(), andpeekNext().

Item QHashIterator::previous()

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

Callkey() on the return value to obtain the item's key, andvalue() to obtain the value.

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

See alsohasPrevious(),peekPrevious(), andnext().

void QHashIterator::toBack()

Moves the iterator to the back of the container (after the last item).

See alsotoFront() andprevious().

void QHashIterator::toFront()

Moves the iterator to the front of the container (before the first item).

See alsotoBack() andnext().

constT & QHashIterator::value() const

Returns the value of the last item that was jumped over using one of the traversal functions (next(),previous(),findNext(),findPrevious()).

After a call tonext() orfindNext(), value() is equivalent topeekPrevious().value(). After a call toprevious() orfindPrevious(), value() is equivalent topeekNext().value().

See alsokey().

QHashIterator & QHashIterator::operator=(constQHash<Key,T> & hash)

Makes the iterator operate onhash. The iterator is set to be at the front of the hash (before the first item).

See alsotoFront() andtoBack().