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Qt 4.8
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Qt 4.8
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The QHash::iterator class provides an STL-style non-const iterator for QHash and QMultiHash. More...
#include <qhash.h>
Public Types | |
| typedef qptrdiff | difference_type |
| typedef std::bidirectional_iterator_tag | iterator_category |
| typedef T * | pointer |
| typedef T & | reference |
| typedef T | value_type |
Public Functions | |
| iterator () | |
| Constructs an uninitialized iterator. More... | |
| iterator (void *node) | |
| const Key & | key () const |
| Returns the current item's key as a const reference. More... | |
| operator Node * () const | |
| bool | operator!= (const iterator &o) const |
| Returns true if other points to a different item than this iterator; otherwise returns false. More... | |
| bool | operator!= (const const_iterator &o) const |
| T & | operator* () const |
| Returns a modifiable reference to the current item's value. More... | |
| iterator | operator+ (int j) const |
| Returns an iterator to the item at j positions forward from this iterator. More... | |
| iterator & | operator++ () |
The prefix ++ operator (++i) advances the iterator to the next item in the hash and returns an iterator to the new current item. More... | |
| iterator | operator++ (int) |
The postfix ++ operator (i++) advances the iterator to the next item in the hash and returns an iterator to the previously current item. More... | |
| iterator & | operator+= (int j) |
| Advances the iterator by j items. More... | |
| iterator | operator- (int j) const |
| Returns an iterator to the item at j positions backward from this iterator. More... | |
| iterator & | operator-- () |
The prefix – operator (–i) makes the preceding item current and returns an iterator pointing to the new current item. More... | |
| iterator | operator-- (int) |
The postfix – operator (i–) makes the preceding item current and returns an iterator pointing to the previously current item. More... | |
| iterator & | operator-= (int j) |
| Makes the iterator go back by j items. More... | |
| T * | operator-> () const |
| Returns a pointer to the current item's value. More... | |
| bool | operator== (const iterator &o) const |
| Returns true if other points to the same item as this iterator; otherwise returns false. More... | |
| bool | operator== (const const_iterator &o) const |
| T & | value () const |
| Returns a modifiable reference to the current item's value. More... | |
Private Functions | |
| operator bool () const | |
Properties | |
| QHashData::Node * | i |
Friends | |
| class | const_iterator |
The QHash::iterator class provides an STL-style non-const iterator for QHash and QMultiHash.
QHash features 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.
QHash<Key, T>::iterator allows you to iterate over a QHash (or QMultiHash) and to modify the value (but not the key) associated with a particular key. If you want to iterate over a const QHash, you should use QHash::const_iterator. It is generally good practice to use QHash::const_iterator on a non-const QHash as well, unless you need to change the QHash through the iterator. Const iterators are slightly faster, and can improve code readability.
The default QHash::iterator constructor creates an uninitialized iterator. You must initialize it using a QHash function like QHash::begin(), QHash::end(), or QHash::find() before you can start iterating. Here's a typical loop that prints all the (key, value) pairs stored in a hash:
Unlike QMap, which orders its items by key, QHash stores its items in an arbitrary order. The only guarantee is that items that share the same key (because they were inserted using QHash::insertMulti()) will appear consecutively, from the most recently to the least recently inserted value.
Let's see a few examples of things we can do with a QHash::iterator that we cannot do with a QHash::const_iterator. Here's an example that increments every value stored in the QHash by 2:
Here's an example that removes all the items whose key is a string that starts with an underscore character:
The call to QHash::erase() removes the item pointed to by the iterator from the hash, and returns an iterator to the next item. Here's another way of removing an item while iterating:
It might be tempting to write code like this:
However, this will potentially crash in ++i, because i is a dangling iterator after the call to erase().
Multiple iterators can be used on the same hash. However, be aware that any modification performed directly on the QHash has the potential of dramatically changing the order in which the items are stored in the hash, as they might cause QHash to rehash its internal data structure. There is one notable exception: QHash::erase(). This function can safely be called while iterating, and won't affect the order of items in the hash. If you need to keep iterators over a long period of time, we recommend that you use QMap rather than QHash.
| QHash< Key, T >::iterator::difference_type |
| QHash< Key, T >::iterator::iterator_category |
| QHash< Key, T >::iterator::pointer |
| QHash< Key, T >::iterator::reference |
| QHash< Key, T >::iterator::value_type |
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Constructs an uninitialized iterator.
Functions like key(), value(), and operator++() must not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.
Definition at line 344 of file qhash.h.
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Returns the current item's key as a const reference.
There is no direct way of changing an item's key through an iterator, although it can be done by calling QHash::erase() followed by QHash::insert() or QHash::insertMulti().
Definition at line 347 of file qhash.h.
Referenced by QScriptDebuggerCodeWidgetPrivate::_q_onScriptsChanged(), QGraphicsScenePrivate::cancelGesturesForChildren(), QMetaObject::changeGuard(), QObjectPrivate::clearGuards(), QTextureGlyphCache::fillInPendingGlyphs(), QMultiHash< const QGLContext *, GLProgram >::find(), QCache< QPixmapCache::Key, QPixmapCacheEntry >::insert(), QAbstractItemModelPrivate::Persistent::insertMultiAtEnd(), ModelNode::object(), qDBusRemoveTimeout(), QDeclarativeDebugConnectionPrivate::readyRead(), QDeclarativeDebugServer::receiveMessage(), QMultiHash< const QGLContext *, GLProgram >::remove(), QMainWindowLayout::removeFromMacToolbar(), QMetaObject::removeGuard(), QGtkStylePrivate::removeWidgetFromMap(), QApplication::syncX(), QPollingFileSystemWatcherEngine::timeout(), QMenuPrivate::QMacMenuPrivate::~QMacMenuPrivate(), and QMenu::~QMenu().
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Returns an iterator to the item at j positions forward from this iterator.
(If j is negative, the iterator goes backward.)
This operation can be slow for large j values.
Definition at line 372 of file qhash.h.
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The prefix ++ operator (++i) advances the iterator to the next item in the hash and returns an iterator to the new current item.
Calling this function on QHash::end() leads to undefined results.
Definition at line 354 of file qhash.h.
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The postfix ++ operator (i++) advances the iterator to the next item in the hash and returns an iterator to the previously current item.
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Definition at line 358 of file qhash.h.
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Advances the iterator by j items.
(If j is negative, the iterator goes backward.)
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Returns an iterator to the item at j positions backward from this iterator.
(If j is negative, the iterator goes forward.)
This operation can be slow for large j values.
Definition at line 374 of file qhash.h.
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The prefix – operator (–i) makes the preceding item current and returns an iterator pointing to the new current item.
Calling this function on QHash::begin() leads to undefined results.
Definition at line 363 of file qhash.h.
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The postfix – operator (i–) makes the preceding item current and returns an iterator pointing to the previously current item.
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Definition at line 367 of file qhash.h.
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Makes the iterator go back by j items.
(If j is negative, the iterator goes forward.)
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Returns a modifiable reference to the current item's value.
You can change the value of an item by using value() on the left side of an assignment, for example:
Definition at line 348 of file qhash.h.
Referenced by QApplicationPrivate::_q_alertTimeOut(), QScriptEnginePrivate::_q_objectDestroyed(), QNetworkConfigurationManagerPrivate::allConfigurations(), QGLGlyphCache::cacheGlyphs(), QGraphicsScenePrivate::cancelGesturesForChildren(), QProcessManager::catchDeadChildren(), QMetaObject::changeGuard(), QGLGlyphCache::cleanCache(), QAxBase::clear(), QObjectPrivate::clearGuards(), QNetworkConfigurationManagerPrivate::defaultConfiguration(), QTextureGlyphCache::fillInPendingGlyphs(), QAuServerQWS::find(), QMultiHash< const QGLContext *, GLProgram >::find(), QNetworkDiskCache::insert(), QCache< QPixmapCache::Key, QPixmapCacheEntry >::insert(), QPaintBufferResource::insert(), qDBusRemoveTimeout(), QDeclarativeDebugConnectionPrivate::readyRead(), QDeclarativeDebugServer::receiveMessage(), QItemEditorFactory::registerEditor(), QPaintBufferResource::remove(), QMultiHash< const QGLContext *, GLProgram >::remove(), QMainWindowLayout::removeFromMacToolbar(), QMetaObject::removeGuard(), QGraphicsScenePrivate::removeItemHelper(), QApplication::syncX(), QPollingFileSystemWatcherEngine::timeout(), QEventDispatcherMac::unregisterTimers(), QPaintBufferResource::value(), QBearerEngine::~QBearerEngine(), QDeclarativeDebugConnection::~QDeclarativeDebugConnection(), QDeclarativeEngineDebugPrivate::~QDeclarativeEngineDebugPrivate(), QEventDispatcherMac::~QEventDispatcherMac(), QMenuPrivate::QMacMenuPrivate::~QMacMenuPrivate(), QMenu::~QMenu(), QPageSetupDialogPrivate::~QPageSetupDialogPrivate(), and QPrintDialogPrivate::~QPrintDialogPrivate().
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Definition at line 333 of file qhash.h.
Referenced by QHash< Key, T >::const_iterator::const_iterator(), QHash< Key, T >::iterator::operator!=(), and QHash< Key, T >::iterator::operator==().