Contents

• Public Functions
• Detailed Description

Detailed Description

TheQMutableHashIterator class provides a Java-style non-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.

QMutableHashIterator<Key, T> allows you to iterate over aQHash (or aQMultiHash) and modify the hash. If you don't want to modify the hash (or have a constQHash), use the slightly fasterQHashIterator instead.

TheQMutableHashIterator 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;...QMutableHashIterator<QString,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:

QMutableHashIterator<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:

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

If you want to remove items as you iterate over the hash, useremove(). If you want to modify the value of an item, usesetValue().

Example:

QMutableHashIterator<QString,QString> i(hash);while (i.hasNext()) {    i.next();if (i.key()== i.value())        i.remove();}

The example removes all (key, value) pairs where the key and the value are the same.

Only one mutable iterator can be active on a given hash at any time. Furthermore, no changes should be done directly to the hash while the iterator is active (as opposed to through the iterator), since this could invalidate the iterator and lead to undefined behavior.

Member Function Documentation

QMutableHashIterator::QMutableHashIterator(QHash<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=().

QMutableHashIterator::~QMutableHashIterator()

Destroys the iterator.

See alsooperator=().

bool QMutableHashIterator::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 QMutableHashIterator::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 QMutableHashIterator::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 QMutableHashIterator::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 & QMutableHashIterator::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 QMutableHashIterator::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 QMutableHashIterator::peekNext() const

Returns a reference to 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 QMutableHashIterator::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 QMutableHashIterator::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 QMutableHashIterator::remove()

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

See alsosetValue().

void QMutableHashIterator::setValue(constT & value)

Replaces the value of the last item that was jumped over using one of the traversal functions withvalue.

The traversal functions arenext(),previous(),findNext(), andfindPrevious().

See alsokey(),value(), andremove().

void QMutableHashIterator::toBack()

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

See alsotoFront() andprevious().

void QMutableHashIterator::toFront()

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

See alsotoBack() andnext().

constT & QMutableHashIterator::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() andsetValue().

T & QMutableHashIterator::value()

This is an overloaded function.

Returns a non-const reference to the value of the last item that was jumped over using one of the traversal functions.

QMutableHashIterator & QMutableHashIterator::operator=(QHash<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().