QMultiHash< Key, T > Class Template Reference

The QMultiHash class is a convenience QHash subclass that provides multi-valued hashes. More...

#include <qcontainerfwd.h>

Inheritance diagram for QMultiHash< Key, T >:

Public Functions
QHash< Key, T >::const_iterator	constFind (const Key &key, const T &value) const
	Returns an iterator pointing to the item with the key and the value in the hash. More...
bool	contains (const Key &key, const T &value) const
	Returns true if the hash contains an item with the key and value; otherwise returns false. More...
int	count (const Key &key, const T &value) const
	Returns the number of items with the key and value. More...
QHash< Key, T >::iterator	find (const Key &key, const T &value)
	Returns an iterator pointing to the item with the key and value. More...
QHash< Key, T >::const_iterator	find (const Key &key, const T &value) const
QHash< Key, T >::iterator	insert (const Key &key, const T &value)
	Inserts a new item with the key and a value of value. More...
QMultiHash	operator+ (const QMultiHash &other) const
	Returns a hash that contains all the items in this hash in addition to all the items in other. More...
QMultiHash &	operator+= (const QMultiHash &other)
	Inserts all the items in the other hash into this hash and returns a reference to this hash. More...
	QMultiHash ()
	Constructs an empty hash. More...
	QMultiHash (const QHash< Key, T > &other)
	Constructs a copy of other (which can be a QHash or a QMultiHash). More...
int	remove (const Key &key, const T &value)
	Removes all the items that have the key and the value value from the hash. More...
QHash< Key, T >::iterator	replace (const Key &key, const T &value)
	Inserts a new item with the key and a value of value. More...
void	swap (QMultiHash< Key, T > &other)
	Swaps hash other with this hash. More...
Public Functions inherited from QHash< Key, T >
iterator	begin ()
	Returns an STL-style iterator pointing to the first item in the hash. More...
const_iterator	begin () const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. More...
int	capacity () const
	Returns the number of buckets in the QHash's internal hash table. More...
void	clear ()
	Removes all items from the hash. More...
const_iterator	constBegin () const
	Returns a const STL-style iterator pointing to the first item in the hash. More...
const_iterator	constEnd () const
	Returns a const STL-style iterator pointing to the imaginary item after the last item in the hash. More...
const_iterator	constFind (const Key &key) const
	Returns an iterator pointing to the item with the key in the hash. More...
bool	contains (const Key &key) const
	Returns true if the hash contains an item with the key; otherwise returns false. More...
int	count (const Key &key) const
	Returns the number of items associated with the key. More...
int	count () const
	Same as size(). More...
void	detach ()
	Detaches this hash from any other hashes with which it may share data. More...
bool	empty () const
	This function is provided for STL compatibility. More...
iterator	end ()
	Returns an STL-style iterator pointing to the imaginary item after the last item in the hash. More...
const_iterator	end () const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. More...
iterator	erase (iterator it)
	Removes the (key, value) pair associated with the iterator pos from the hash, and returns an iterator to the next item in the hash. More...
iterator	find (const Key &key)
	Returns an iterator pointing to the item with the key in the hash. More...
const_iterator	find (const Key &key) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. More...
iterator	insert (const Key &key, const T &value)
	Inserts a new item with the key and a value of value. More...
iterator	insertMulti (const Key &key, const T &value)
	Inserts a new item with the key and a value of value. More...
bool	isDetached () const
	Returns true if the hash's internal data isn't shared with any other hash object; otherwise returns false. More...
bool	isEmpty () const
	Returns true if the hash contains no items; otherwise returns false. More...
bool	isSharedWith (const QHash< Key, T > &other) const
const Key	key (const T &value) const
	Returns the first key mapped to value. More...
const Key	key (const T &value, const Key &defaultKey) const
	Returns the first key mapped to value, or defaultKey if the hash contains no item mapped to value. More...
QList< Key >	keys () const
	Returns a list containing all the keys in the hash, in an arbitrary order. More...
QList< Key >	keys (const T &value) const
	Returns a list containing all the keys associated with value value, in an arbitrary order. More...
bool	operator!= (const QHash< Key, T > &other) const
	Returns true if other is not equal to this hash; otherwise returns false. More...
QHash< Key, T > &	operator= (const QHash< Key, T > &other)
	Assigns other to this hash and returns a reference to this hash. More...
bool	operator== (const QHash< Key, T > &other) const
	Returns true if other is equal to this hash; otherwise returns false. More...
T &	operator[] (const Key &key)
	Returns the value associated with the key as a modifiable reference. More...
const T	operator[] (const Key &key) const
	Same as value(). More...
	QHash ()
	Constructs an empty hash. More...
	QHash (const QHash< Key, T > &other)
	Constructs a copy of other. More...
int	remove (const Key &key)
	Removes all the items that have the key from the hash. More...
void	reserve (int size)
	Ensures that the QHash's internal hash table consists of at least size buckets. More...
void	setSharable (bool sharable)
int	size () const
	Returns the number of items in the hash. More...
void	squeeze ()
	Reduces the size of the QHash's internal hash table to save memory. More...
void	swap (QHash< Key, T > &other)
	Swaps hash other with this hash. More...
T	take (const Key &key)
	Removes the item with the key from the hash and returns the value associated with it. More...
QList< Key >	uniqueKeys () const
	Returns a list containing all the keys in the map. More...
QHash< Key, T > &	unite (const QHash< Key, T > &other)
	Inserts all the items in the other hash into this hash. More...
const T	value (const Key &key) const
	Returns the value associated with the key. More...
const T	value (const Key &key, const T &defaultValue) const
	If the hash contains no item with the given key, the function returns defaultValue. More...
QList< T >	values () const
	Returns a list containing all the values in the hash, in an arbitrary order. More...
QList< T >	values (const Key &key) const
	Returns a list of all the values associated with the key, from the most recently inserted to the least recently inserted. More...
	~QHash ()
	Destroys the hash. More...

Private Functions
T &	operator[] (const Key &key)
const T	operator[] (const Key &key) const

Additional Inherited Members
Public Types inherited from QHash< Key, T >
typedef const_iterator	ConstIterator
	Qt-style synonym for QHash::const_iterator. More...
typedef qptrdiff	difference_type
	Typedef for ptrdiff_t. More...
typedef iterator	Iterator
	Qt-style synonym for QHash::iterator. More...
typedef Key	key_type
	Typedef for Key. More...
typedef T	mapped_type
	Typedef for T. More...
typedef int	size_type
	Typedef for int. More...
Related Functions inherited from QHash< Key, T >
QDataStream &	operator<< (QDataStream &out, const QHash< Key, T > &hash)
	Writes the hash hash to stream out. More...
QDataStream &	operator>> (QDataStream &in, QHash< Key, T > &hash)
	Reads a hash from stream in into hash. More...
uint	qHash (const QPair< T1, T2 > &key)
	Returns the hash value for the key. More...
uint	qHash (char key)
	Returns the hash value for the key. More...
uint	qHash (uchar key)
	Returns the hash value for the key. More...
uint	qHash (signed char key)
	Returns the hash value for the key. More...
uint	qHash (ushort key)
	Returns the hash value for the key. More...
uint	qHash (short key)
	Returns the hash value for the key. More...
uint	qHash (uint key)
	Returns the hash value for the key. More...
uint	qHash (int key)
	Returns the hash value for the key. More...
uint	qHash (ulong key)
	Returns the hash value for the key. More...
uint	qHash (long key)
	Returns the hash value for the key. More...
uint	qHash (quint64 key)
	Returns the hash value for the key. More...
uint	qHash (qint64 key)
	Returns the hash value for the key. More...
uint	qHash (QChar key)
	Returns the hash value for the key. More...
uint	qHash (const QBitArray &key)
uint	qHash (const QString &key)
	Returns the hash value for the key. More...
uint	qHash (const T *key)
uint	qHash (const QXmlNodeModelIndex &index)
	Computes a hash key from the QXmlNodeModelIndex index, and returns it. More...

Detailed Description

template<class Key, class T>
class QMultiHash< Key, T >

The QMultiHash class is a convenience QHash subclass that provides multi-valued hashes.

Note

This class or function is reentrant.

QMultiHash<Key, T> is one of Qt's generic container classes. It inherits QHash and extends it with a few convenience functions that make it more suitable than QHash for storing multi-valued hashes. A multi-valued hash is a hash that allows multiple values with the same key; QHash normally doesn't allow that, unless you call QHash::insertMulti().

Because QMultiHash inherits QHash, all of QHash's functionality also applies to QMultiHash. For example, you can use isEmpty() to test whether the hash is empty, and you can traverse a QMultiHash using QHash's iterator classes (for example, QHashIterator). But in addition, it provides an insert() function that corresponds to QHash::insertMulti(), and a replace() function that corresponds to QHash::insert(). It also provides convenient operator+() and operator+=().

Example:

QMultiHash<QString, int> hash1, hash2, hash3;

hash1.insert("plenty", 100);
hash1.insert("plenty", 2000);
// hash1.size() == 2

hash2.insert("plenty", 5000);
// hash2.size() == 1

hash3 = hash1 + hash2;
// hash3.size() == 3

Unlike QHash, QMultiHash provides no operator[]. Use value() or replace() if you want to access the most recently inserted item with a certain key.

If you want to retrieve all the values for a single key, you can use values(const Key &key), which returns a QList<T>:

QList<int> values = hash.values("plenty");
for (int i = 0; i < values.size(); ++i)
    cout << values.at(i) << endl;

The items that share the same key are available from most recently to least recently inserted.

A more efficient approach is to call find() to get the STL-style iterator for the first item with a key and iterate from there:

QMultiHash<QString, int>::iterator i = hash.find("plenty");
while (i != hash.end() && i.key() == "plenty") {
    cout << i.value() << endl;
    ++i;
}

QMultiHash's key and value data types must be assignable data types. You cannot, for example, store a QWidget as a value; instead, store a QWidget *. In addition, QMultiHash's key type must provide operator==(), and there must also be a global qHash() function that returns a hash value for an argument of the key's type. See the QHash documentation for details.

See also

QHash, QHashIterator, QMutableHashIterator, QMultiMap

Definition at line 58 of file qcontainerfwd.h.

Constructors and Destructors

QMultiHash() [1/2]

template<class Key, class T>

QMultiHash< Key, T >::QMultiHash ( )

inline

Constructs an empty hash.

Definition at line 927 of file qhash.h.

{}

QMultiHash() [2/2]

template<class Key, class T>

QMultiHash< Key, T >::QMultiHash ( const QHash< Key, T > &  other )

inline

Constructs a copy of other (which can be a QHash or a QMultiHash).

See also

operator=()

Definition at line 928 of file qhash.h.

: QHash<Key, T>(other) {}

Functions

constFind()

template<class Key, class T>

typename QHash< Key, T >::const_iterator QMultiHash< Key, T >::constFind ( const Key &  key, const T &  value  ) const

inline

Returns an iterator pointing to the item with the key and the value in the hash.

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Since

4.3

If the hash contains no such item, the function returns constEnd().

See also

QHash::constFind()

QHash::constFind()

Definition at line 992 of file qhash.h.

Referenced by QDBusConnectionPrivate::socketRead(), and QDBusConnectionPrivate::socketWrite().

        { return find(key, value); }

contains()

template<class Key, class T>

Q_INLINE_TEMPLATE bool QMultiHash< Key, T >::contains	(	const Key &	key,
		const T &	value
	)		const

Returns true if the hash contains an item with the key and value; otherwise returns false.

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Since

4.3

See also

QHash::contains()

QHash::contains()

Definition at line 1000 of file qhash.h.

{
    return constFind(key, value) != QHash<Key, T>::constEnd();
}

count()

template<class Key, class T>

Q_INLINE_TEMPLATE int QMultiHash< Key, T >::count	(	const Key &	key,
		const T &	value
	)		const

Returns the number of items with the key and value.

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Since

4.3

See also

QHash::count()

QHash::count()

Definition at line 1023 of file qhash.h.

Referenced by QGraphicsAnchorLayoutPrivate::constraintsFromPaths().

{
    int n = 0;
    typename QHash<Key, T>::const_iterator i(constFind(key));
    typename QHash<Key, T>::const_iterator end(QHash<Key, T>::constEnd());
    while (i != end && i.key() == key) {
        if (i.value() == value)
            ++n;
        ++i;
    }
    return n;
}

find() [1/2]

template<class Key, class T>

typename QHash< Key, T >::iterator QMultiHash< Key, T >::find ( const Key &  key, const T &  value  )

inline

Returns an iterator pointing to the item with the key and value.

Since

4.3

If the hash contains no such item, the function returns end().

If the hash contains multiple items with the key and value, the iterator returned points to the most recently inserted item.

See also

QHash::find()

Definition at line 972 of file qhash.h.

Referenced by QMetaObject::changeGuard(), QObjectPrivate::clearGuards(), QDBusConnectionPrivate::connectRelay(), QDBusConnectionPrivate::connectSignal(), QDBusConnectionPrivate::disconnectRelay(), QDBusConnectionPrivate::disconnectSignal(), QDBusConnectionPrivate::handleSignal(), QTextFormatCollection::hasFormatCached(), QTextFormatCollection::indexForFormat(), qDBusRealToggleWatch(), qDBusRemoveWatch(), and QMetaObject::removeGuard().

                                                                        {
        typename QHash<Key, T>::iterator i(find(key));
        typename QHash<Key, T>::iterator end(this->end());
        while (i != end && i.key() == key) {
            if (i.value() == value)
                return i;
            ++i;
        }
        return end;
    }

find() [2/2]

template<class Key, class T>

typename QHash< Key, T >::const_iterator QMultiHash< Key, T >::find ( const Key &  key, const T &  value  ) const

inline

Since

4.3 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 982 of file qhash.h.

                                                                                    {
        typename QHash<Key, T>::const_iterator i(constFind(key));
        typename QHash<Key, T>::const_iterator end(QHash<Key, T>::constEnd());
        while (i != end && i.key() == key) {
            if (i.value() == value)
                return i;
            ++i;
        }
        return end;
    }

insert()

template<class Key, class T>

QMultiHash::iterator QMultiHash< Key, T >::insert ( const Key &  key, const T &  value  )

inline

Inserts a new item with the key and a value of value.

If there is already an item with the same key in the hash, this function will simply create a new one. (This behavior is different from replace(), which overwrites the value of an existing item.)

See also

replace()

Definition at line 934 of file qhash.h.

Referenced by QMetaObject::changeGuard(), QIcdEngine::doRequestUpdate(), QGraphicsAnchorLayoutPrivate::findPaths(), and QDBusConnectionPrivate::setConnection().

    { return QHash<Key, T>::insertMulti(key, value); }

operator+()

template<class Key, class T>

QMultiHash QMultiHash< Key, T >::operator+ ( const QMultiHash< Key, T > &  other ) const

inline

Returns a hash that contains all the items in this hash in addition to all the items in other.

If a key is common to both hashes, the resulting hash will contain the key multiple times.

See also

operator+=()

Definition at line 939 of file qhash.h.

    { QMultiHash result = *this; result += other; return result; }

operator+=()

template<class Key, class T>

QMultiHash & QMultiHash< Key, T >::operator+= ( const QMultiHash< Key, T > &  other )

inline

Inserts all the items in the other hash into this hash and returns a reference to this hash.

See also

insert()

Definition at line 937 of file qhash.h.

    { this->unite(other); return *this; }

operator[]() [1/2]

template<class Key, class T>

T& QMultiHash< Key, T >::operator[] ( const Key &  key )

private

operator[]() [2/2]

template<class Key, class T>

const T QMultiHash< Key, T >::operator[] ( const Key &  key ) const

private

remove()

template<class Key, class T>

Q_INLINE_TEMPLATE int QMultiHash< Key, T >::remove	(	const Key &	key,
		const T &	value
	)

Removes all the items that have the key and the value value from the hash.

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Since

4.3

Returns the number of items removed.

See also

QHash::remove()

QHash::remove()

Definition at line 1006 of file qhash.h.

Referenced by QIcdEngine::doRequestUpdate().

{
    int n = 0;
    typename QHash<Key, T>::iterator i(find(key));
    typename QHash<Key, T>::iterator end(QHash<Key, T>::end());
    while (i != end && i.key() == key) {
        if (i.value() == value) {
            i = this->erase(i);
            ++n;
        } else {
            ++i;
        }
    }
    return n;
}

replace()

template<class Key, class T>

QMultiHash::iterator QMultiHash< Key, T >::replace ( const Key &  key, const T &  value  )

inline

Inserts a new item with the key and a value of value.

If there is already an item with the key, that item's value is replaced with value.

If there are multiple items with the key, the most recently inserted item's value is replaced with value.

See also

insert()

Definition at line 931 of file qhash.h.

    { return QHash<Key, T>::insert(key, value); }

swap()

template<class Key, class T>

void QMultiHash< Key, T >::swap ( QMultiHash< Key, T > &  other )

inline

Swaps hash other with this hash.

Since

4.8

This operation is very fast and never fails.

Definition at line 929 of file qhash.h.

{ QHash<Key, T>::swap(other); } // prevent QMultiHash<->QHash swaps

---

The documentation for this class was generated from the following files:

• /src/corelib/tools/qcontainerfwd.h
• /src/corelib/tools/qhash.h
• /src/corelib/tools/qhash.cpp