Template class which provides an unordered container of keys and values. More...

Classes
class	const_iterator
	STL style const iterator for QHash More...

class	iterator
	STL style non-const iterator for QHash More...

Public Typedefs
using	const_pointer = const Val *

using	const_reference = const Val &

using	difference_type = typename std::unordered_map< Key, Val, Hash, KeyEqual >::difference_type

using	hasher = typename std::unordered_map< Key, Val, Hash, KeyEqual >::hasher

using	key_equal = typename std::unordered_map< Key, Val, Hash, KeyEqual >::key_equal

using	key_type = typename std::unordered_map< Key, Val, Hash, KeyEqual >::key_type

using	mapped_type = typename std::unordered_map< Key, Val, Hash, KeyEqual >::mapped_type

using	pointer = Val *

using	reference = Val &

using	size_type = typename std::unordered_map< Key, Val, Hash, KeyEqual >::difference_type

using	value_type = Val

Public Methods
	QHash () = default

	QHash (const Hash &hash, const KeyEqual &key_equal=KeyEqual ())

	QHash (const QHash< Key, Val, Hash, KeyEqual > &other) = default

	QHash (const std::unordered_map< Key, Val, Hash, KeyEqual > &other)

template<typename Input_Iterator >
	QHash (Input_Iterator first, Input_Iterator last, const Hash &hash=Hash (), const KeyEqual &key_equal=KeyEqual ())

	QHash (QHash< Key, Val, Hash, KeyEqual > &&other) = default

	QHash (std::initializer_list< std::pair< const Key, Val >> list, const Hash &hash=Hash (), const KeyEqual &key_equal=KeyEqual ())

	QHash (std::unordered_map< Key, Val, Hash, KeyEqual > &&other)

	~QHash () = default

iterator	begin ()

const_iterator	begin () const

size_type	capacity () const

const_iterator	cbegin () const

const_iterator	cend () const

void	clear ()

const_iterator	constBegin () const

const_iterator	constEnd () const

const_iterator	constFind (const Key &key) const

bool	contains (const Key &key) const

size_type	count () const

size_type	count (const Key &key) const

bool	empty () const

iterator	end ()

const_iterator	end () const

QPair< iterator, iterator >	equal_range (const Key &key)

QPair< const_iterator, const_iterator >	equal_range (const Key &key) const

iterator	erase (const_iterator iter)

iterator	find (const Key &key)

const_iterator	find (const Key &key) const

iterator	insert (const Key &key, const Val &value)

iterator	insert (const std::pair< const Key, Val > &data)

bool	isEmpty () const

const Key	key (const Val &value) const

const Key	key (const Val &value, const Key &defaultKey) const

QList< Key >	keys () const

QList< Key >	keys (const Val &value) const

bool	operator!= (const QHash< Key, Val, Hash, KeyEqual > &other) const

QHash< Key, Val, Hash, KeyEqual > &	operator= (const QHash< Key, Val, Hash, KeyEqual > &other) = default

QHash< Key, Val, Hash, KeyEqual > &	operator= (QHash< Key, Val, Hash, KeyEqual > &&other) = default

bool	operator== (const QHash< Key, Val, Hash, KeyEqual > &other) const

Val &	operator[] (const Key &key)

const Val	operator[] (const Key &key) const

size_type	remove (const Key &key)

void	reserve (size_type size)

size_type	size () const

void	squeeze ()

void	swap (QHash< Key, Val, Hash, KeyEqual > &other)

Val	take (const Key &key)

QHash< Key, Val, Hash, KeyEqual > &	unite (const QHash< Key, Val, Hash, KeyEqual > &other)

Val	value (const Key &key) const

Val	value (const Key &key, const Val &defaultValue) const

QList< Val >	values () const

Related Functions
These are not member functions
QDataStream &	operator<< (QDataStream &stream, const QHash< Key, Val, Hash, KeyEqual > &hash)

QDataStream &	operator>> (QDataStream &stream, QHash< Key, Val, Hash, KeyEqual > &hash)

uint	qHash (char key)

uint	qHash (const QBitArray &key)

uint	qHash (const QByteArray &key)

uint	qHash (const QHostAddress &key, uint seed=0)

uint	qHash (const QItemSelectionRange &key, uint seed=0)

uint	qHash (const QList< T > &key, uint seed=0)

uint	qHash (const QPair< T1, T2 > &key)

uint	qHash (const QSharedPointer< T > &ptr, uint seed=0)

uint	qHash (const QSourceLocation &location)

uint	qHash (const QSslError &key, uint seed)

uint	qHash (const QString &key)

uint	qHash (const QTransform &key, uint seed=0)

uint	qHash (const QUrl &key, uint seed=0)

uint	qHash (const QUrlQuery &key, uint seed=0)

uint	qHash (const QVector< T > &key, uint seed=0)

uint	qHash (const QXmlName &name)

uint	qHash (const QXmlNodeModelIndex &index)

uint	qHash (const T *key)

uint	qHash (int key)

uint	qHash (long key)

uint	qHash (QChar key)

uint	qHash (qint64 key)

uint	qHash (QSslEllipticCurve curve, uint seed=0)

uint	qHash (quint64 key)

uint	qHash (short key)

uint	qHash (signed char key)

uint	qHash (uchar key)

uint	qHash (uint key)

uint	qHash (ulong key)

uint	qHash (ushort key)

Detailed Description

template<typename Key, typename Val, typename Hash, typename KeyEqual>
class QHash< Key, Val, Hash, KeyEqual >

The QHash class is a template class which provides an unordered container of keys and values. This container stores the key and value as a pair. For a given key there is one corresponding value.

Elements in a QMap are sorted by key, elements in a QHash are in an arbitrary order/li>
QHash provides faster lookups than a QMap or a QFlatMap
The key data type for a QHash must implement the operator==() method and a global qHash(key) function
The key data type for a QMap must implement the operator<() method
Use QFlatMap when your data set is relatively small

For an overview and comparison of all containers, refer to the documentation for Container Classes. Refer to the section on Time Complexity for a discussion about which operations will be relatively faster or slower for a given container with a size of n.

Constructors

The following code is a simple example showing how to declare a QHash.

QHash<QString, int> hash; // stores QString key and int values

Accessing Elements

To insert a (key, value) pair into the hash use operator[]. This example inserts the following three (key, value) pairs into the QHash: ("one", 1), ("three", 3), and ("seven", 7).

QHash<QString, int> hash;
 
hash["one"]   = 1;
hash["three"] = 3;
hash["seven"] = 7;

Another way to insert items into the hash is to use the insert() method.

hash.insert("twelve", 12);

The following are examples to look up a value using the operator[] or value() methods.

int num1 = hash["thirteen"]; // if the key is not present ("thirteen", 0) will be inserted

int num2 = hash.value("thirteen");

If you want to check whether the hash contains a particular key use the method contains().

int timeout = 30;
 
if (hash.contains("TIMEOUT")) {
   timeout = hash.value("TIMEOUT");
}

There is an overload for value() which accepts a second argument as a default value if there is no item with the specified key.

int timeout = hash.value("TIMEOUT", 30);

In general you should use contains() and value() rather than operator[]() for looking up a key in a hash. The reason is operator[]() silently inserts an item into the hash if no item exists with the same key (unless the hash is const). For example, the following code will create 1000 items in memory.

// incorrect
QHash<int, QWidget *> hash;
 
for (int i = 0; i < 1000; ++i) {
   if (hash[i] == okButton) {
      cout << "Found button at index " << i << endl;
   }
}

To avoid this problem, replace hash[i] with hash.value(i) in the code above.

Iterators

To navigate through all (key, value) pairs stored in a QHash use an iterator. QHash provides both Java style iterators (QHashIterator and QMutableHashIterator) and STL style iterators (QHash::const_iterator and QHash::iterator).

The following shows how to iterate over a QHash<QString, int> using a Java style iterator.

QHashIterator<QString, int> iter(hash);
 
while (iter.hasNext()) {
    iter.next();
    cout << iter.key() << ": " << iter.value() << endl;
}

Here is the same code using an STL style iterator.

QHash<QString, int>::const_iterator iter = hash.constBegin();
 
while (iter != hash.constEnd()) {
    cout << iter.key() << ": " << iter.value() << endl;
    ++iter;
}

QHash is unordered so an iterator's sequence can not be assumed to be predictable. If ordering by key is required, use a QMap. QHash only allows only one value per key. To store multiple values for a given key use QMultiHash.

To extract the values from a hash and not the keys then use a range based.

QHash<QString, int> hash;
 
for (int value : hash) {
   cout << value << endl;
}

Items can be removed from the hash in several ways. One way is to call remove() which will remove any item with the given key. Another way is to use QMutableHashIterator::remove(). To clear the entire hash use clear().

Constraints on type T

The QHash<Key, Val> should be Default Constructible and Copy Constructible to work with all methods of this class. Data types like QObject are not copy constructible and therefore should never be stored in a container. You can however use a pointer to a QObject or any subclass as the type T.

The QHash Key type support operator==().

There must also be a global qHash() function which returns a hash value for an argument of the key's type. The following is a list of data types which can serve as keys in a QHash. The <QHash> header file defines qHash() functions which compute hash values for the following data types.

any integer type (char, unsigned long, etc.)
any pointer type
QChar
QString
QByteArray

Comparison Example

If you want to use other data types as the Key, you will need to ensure you provide operator==() and a qHash() implementation.

class Employee
{
   public:
      Employee() = default;
      Employee(const QString &name, const QDate &dateOfBirth);
 
   private:
      QString myName;
      QDate myDateOfBirth;
};
 
bool operator==(const Employee &e1, const Employee &e2) {
   return e1.name() == e2.name() && e1.dateOfBirth() == e2.dateOfBirth();
}
 
uint qHash(const Employee &key) {
   return qHash(key.name()) ^ key.dateOfBirth().day();
}

The qHash() function computes a numeric value based on a key. It can use any algorithm imaginable, as long as it always returns the same value if given the same argument. In other words, if e1 == e2, then qHash(e1) == qHash(e2) must hold as well. However, to obtain good performance, the qHash() function should attempt to return different hash values for different keys to the largest extent possible.

In the example above the CopperSpice global qHash(const QString &) function is used to compute a hash value for the employee's name and it is combined with the day they were born. This will yield a different hash for people with the same name.

Internally, QHash uses a hash table to perform lookups. This hash table automatically grows and shrinks to provide fast lookups. You can control the size of the hash table by calling reserve() if you already know approximately how many items the QHash will contain. This is not necessary to obtain good performance. You can also call capacity() to retrieve the hash table's size.

See also: QMultiHash

Member Typedef Documentation

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::const_pointer

Typedef for const Val *.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::const_reference

Typedef for const Val &.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::difference_type

Typedef for integral type used to represent the distance between two elements.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::hasher

Typedef for the hash object type.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::key_equal

Typedef for the key equality comparison object type.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::key_type

Typedef for Key.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::mapped_type

Typedef for Val.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::pointer

Typedef for Val *.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::reference

Typedef for Val &.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::size_type

Typedef for a signed integer of the appropriate size for your platform.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::value_type

Typedef for Val.

Constructor & Destructor Documentation

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::QHash ( )

default

Constructs an empty QHash.

See also: clear()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::QHash ( const QHash< Key, Val, Hash, KeyEqual > & other )

default

Copy constructs a new QHash from other.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::QHash ( QHash< Key, Val, Hash, KeyEqual > && other )

default

Move constructs a new QHash from other.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::QHash	(	std::initializer_list< std::pair< const Key, Val >>	list,
		const Hash &	hash = `Hash()`,
		const KeyEqual &	key_equal = `KeyEqual()`
	)

inline

Constructs a new QHash with a copy of each of the elements in the initializer list.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::QHash	(	const Hash &	hash,
		const KeyEqual &	key_equal = `KeyEqual()`
	)

inlineexplicit

Constructs a new QHash using the given hash and keyEqual objects.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::QHash ( const std::unordered_map< Key, Val, Hash, KeyEqual > & other )

inlineexplicit

Copy constructs a new QHash from other.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::QHash ( std::unordered_map< Key, Val, Hash, KeyEqual > && other )

inlineexplicit

Move constructs a new QHash from other.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

template<typename Input_Iterator >

QHash< Key, Val, Hash, KeyEqual >::QHash	(	Input_Iterator	first,
		Input_Iterator	last,
		const Hash &	hash = `Hash()`,
		const KeyEqual &	key_equal = `KeyEqual()`
	)

inline

Constructs a hash using the elements between the first and last iterators.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual >::~QHash ( )

default

Destroys this QHash.

Method Documentation

template<typename Key , typename Val , typename Hash , typename KeyEqual >

iterator QHash< Key, Val, Hash, KeyEqual >::begin ( )

inline

Returns an STL style iterator pointing to the first item in the hash.

See also: constBegin(), end()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::begin ( ) const

inline

Returns a cont STL style iterator pointing to the first item in the hash.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

size_type QHash< Key, Val, Hash, KeyEqual >::capacity ( ) const

inline

Returns the number of buckets in the QHash's internal hash table.

The purpose of this method is to provide a means of fine tuning QHash's memory usage. In general, you will rarely ever need to call this method. If you want to know how many items are in the hash call size().

See also: reserve(), squeeze()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::cbegin ( ) const

inline

Returns a const STL style iterator pointing to the first item in the hash.

See also: begin(), cend()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::cend ( ) const

inline

Returns a const STL style iterator pointing to the imaginary item after the last item in the hash.

See also: cbegin(), end()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

void QHash< Key, Val, Hash, KeyEqual >::clear ( )

inline

Removes all items from the hash.

See also: remove()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::constBegin ( ) const

inline

Returns a const STL style iterator pointing to the first item in the hash.

See also: begin(), constEnd()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::constEnd ( ) const

inline

Returns a const STL style iterator pointing to the imaginary item after the last item in the hash.

See also: constBegin(), end()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::constFind ( const Key & key ) const

inline

Returns an iterator pointing to the item with the key in the hash. If the hash contains no item with the key the method returns constEnd().

See also: find()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

bool QHash< Key, Val, Hash, KeyEqual >::contains ( const Key & key ) const

inline

Returns true if the hash contains an item with the key, otherwise it returns false.

See also: count()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

size_type QHash< Key, Val, Hash, KeyEqual >::count ( ) const

inline

Returns the number of items in this hash. Equivalent to calling size().

template<typename Key , typename Val , typename Hash , typename KeyEqual >

size_type QHash< Key, Val, Hash, KeyEqual >::count ( const Key & key ) const

inline

Returns the number of items associated with the key.

See also: contains()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

bool QHash< Key, Val, Hash, KeyEqual >::empty ( ) const

inline

This method is identical to isEmpty(), returning true if the hash is empty otherwise returns false.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

iterator QHash< Key, Val, Hash, KeyEqual >::end ( )

inline

Returns an STL style iterator pointing to the imaginary item after the last item in the hash.

See also: begin(), constEnd()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::end ( ) const

inline

Returns a const STL style iterator pointing to the imaginary item after the last item in the hash.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QPair< iterator, iterator > QHash< Key, Val, Hash, KeyEqual >::equal_range ( const Key & key )

inline

Returns a pair of iterators corresponding to the range of items [first, second) which have the given key. If the range is empty then both iterators will be equal to end().

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QPair< const_iterator, const_iterator > QHash< Key, Val, Hash, KeyEqual >::equal_range ( const Key & key ) const

inline

Returns a pair of iterators corresponding to the range of items [first, second) which have the given key. If the range is empty then both iterators will be equal to end().

template<typename Key , typename Val , typename Hash , typename KeyEqual >

iterator QHash< Key, Val, Hash, KeyEqual >::erase ( const_iterator iter )

inline

Removes the (key, value) pair pointed to by the iterator iter from the hash and returns an iterator to the next item in the hash.

This method assumes the iterator is valid and refers to an element in the hash. It will not check if iter points past the end of the hash or is equal to the end() iterator. This method does not cause QHash to rehash its internal data structure. This means the method can safely be called while iterating and will not affect the order of items in the hash.

QHash<QObject *, int> hash;
QHash<QObject *, int>::iterator iter = hash.find(obj);
 
while (iter != hash.end() && iter.key() == obj) {
 
   if (iter.value() == 0) {
      iter = hash.erase(iter);
   } else {
      ++iter;
   }
}

See also: remove(), take(), find()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

iterator QHash< Key, Val, Hash, KeyEqual >::find ( const Key & key )

inline

Returns an iterator pointing to the item with the key in the hash. If the hash contains no item with the key, the method returns end().

If the hash contains multiple items with the key, this method returns an iterator which points to the most recently inserted value. The other values are accessible by incrementing the iterator. The following is code which iterates over all the items with the same key:

QHash<QString, int> hash;
QHash<QString, int>::const_iterator iter = hash.find("HDR");
 
while (iter != hash.end() && iter.key() == "HDR") {
    cout << iter.value() << endl;
    ++iter;
}

See also: value(), values()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const_iterator QHash< Key, Val, Hash, KeyEqual >::find ( const Key & key ) const

inline

Returns a const iterator pointing to the item with the key in the hash. If the hash contains no item with the key, the method returns end().

template<typename Key , typename Val , typename Hash , typename KeyEqual >

iterator QHash< Key, Val, Hash, KeyEqual >::insert	(	const Key &	key,
		const Val &	value
	)

inline

Inserts a new item with the key and value. If there is already an item with the key, the value for this item is replaced with value.

See also: QMultiHash::insert()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

iterator QHash< Key, Val, Hash, KeyEqual >::insert ( const std::pair< const Key, Val > & data )

inline

Inserts a new item with key and value from data, which is an std::pair. If there is already an item with this key, the value for the item is replaced with value.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

bool QHash< Key, Val, Hash, KeyEqual >::isEmpty ( ) const

inline

Returns true if the hash contains no items, otherwise it returns false.

See also: size()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const Key QHash< Key, Val, Hash, KeyEqual >::key ( const Val & value ) const

Returns the first key mapped to value. If no item with the given value is found then a new value initialized object of type Key is returned. Refer to default constructed elements for additional information.

This method can be slow (linear time) because the internal data structure is optimized for fast lookup by key, not by value.

See also: keys(), value()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const Key QHash< Key, Val, Hash, KeyEqual >::key	(	const Val &	value,
		const Key &	defaultKey
	)		const

Returns the key of the first item matching the given value. Otherwise, returns the given defaultKey.

This method can be slow (linear time) because the internal data structure is optimized for fast lookup by key, not by value.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QList< Key > QHash< Key, Val, Hash, KeyEqual >::keys ( ) const

Returns a list containing all the keys in the hash, in an arbitrary order. The order is guaranteed to be the same as that used by values().

See also: key(), values()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QList< Key > QHash< Key, Val, Hash, KeyEqual >::keys ( const Val & value ) const

Returns a list containing all the keys associated with value, in an arbitrary order.

This method can be slow (linear time), because the internal QHash data structure is optimized for fast lookup by key, not by value.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

bool QHash< Key, Val, Hash, KeyEqual >::operator!= ( const QHash< Key, Val, Hash, KeyEqual > & other ) const

inline

Returns true if other is not equal to this hash otherwise it returns false. Two hashes are considered equal if they contain the same (key, value) pairs. This method requires the type T to support operator==().

See also: operator==()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual > & QHash< Key, Val, Hash, KeyEqual >::operator= ( const QHash< Key, Val, Hash, KeyEqual > & other )

default

Copy assigns from other and returns a reference to this object.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual > & QHash< Key, Val, Hash, KeyEqual >::operator= ( QHash< Key, Val, Hash, KeyEqual > && other )

default

Move assigns from other and returns a reference to this object.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

bool QHash< Key, Val, Hash, KeyEqual >::operator== ( const QHash< Key, Val, Hash, KeyEqual > & other ) const

inline

Returns true if other is equal to this hash, otherwise it returns false. Two hashes are considered equal if they contain the same (key, value) pairs. This method requires the type T to support operator==().

See also: operator!=()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

Val & QHash< Key, Val, Hash, KeyEqual >::operator[] ( const Key & key )

inline

Returns a reference to the value for the element with the given key. If the key was not found then a new value initialized object of type Val with the given key is inserted. A reference to the new element will be returned. Refer to default constructed elements for additional information.

See also: insert(), value()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

const Val QHash< Key, Val, Hash, KeyEqual >::operator[] ( const Key & key ) const

inline

Equivalent to calling value().

template<typename Key , typename Val , typename Hash , typename KeyEqual >

size_type QHash< Key, Val, Hash, KeyEqual >::remove ( const Key & key )

inline

Removes all the items that have the key from the hash. Returns the number of items removed which is usually 1 but will be 0 if the key is not in the hash, or greater than 1 if insertMulti() has been used with the key.

See also: clear(), take()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

void QHash< Key, Val, Hash, KeyEqual >::reserve ( size_type size )

inline

Ensures the internal hash table consists of at least size buckets. This method is useful for code that needs to build a huge hash and wants to avoid repeated reallocation.

QHash<QString, int> hash;
hash.reserve(20000);
 
for (int i = 0; i < 20000; ++i) {
   hash.insert(keys[i], values[i]);
}

Ideally, size should be slightly more than the maximum number of items expected in the hash. The size does not need to be a prime number. If size is underestimate, the QHash will resize automatically.

See also: squeeze(), capacity()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

size_type QHash< Key, Val, Hash, KeyEqual >::size ( ) const

inline

Returns the number of items in the hash.

See also: isEmpty(), count()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

void QHash< Key, Val, Hash, KeyEqual >::squeeze ( )

inline

Reduces the size of the internal hash table to save memory. The purpose of this method is to provide a way to fine tune memory usage. You will rarely need to call this method.

See also: capacity(), reserve()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

void QHash< Key, Val, Hash, KeyEqual >::swap ( QHash< Key, Val, Hash, KeyEqual > & other )

inline

Swaps hash other with this hash. This operation is very fast and never fails.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

Val QHash< Key, Val, Hash, KeyEqual >::take ( const Key & key )

inline

Removes the item with the given key and returns the value. If you do not use the return value remove() is more efficient. If the key was not found then a new value initialized object of type Val with the given key is returned. Refer to default constructed elements for additional information.

See also: remove()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QHash< Key, Val, Hash, KeyEqual > & QHash< Key, Val, Hash, KeyEqual >::unite ( const QHash< Key, Val, Hash, KeyEqual > & other )

inline

Inserts all the items from the other hash into this hash. If a key is common to both hashes, the value in this hash will be retained.

template<typename Key , typename Val , typename Hash , typename KeyEqual >

Val QHash< Key, Val, Hash, KeyEqual >::value ( const Key & key ) const

inline

Returns the value associated with the given key. If no item with the given key is found, a new value initialized object of type Val with the given key is returned. Refer to default constructed elements for additional information.

See also: contains(), key(), values(), operator[]()

template<typename Key , typename Val , typename Hash , typename KeyEqual >

Val QHash< Key, Val, Hash, KeyEqual >::value	(	const Key &	key,
		const Val &	defaultValue
	)		const

inline

Returns the value matching the given key. Otherwise, returns the defaultValue

template<typename Key , typename Val , typename Hash , typename KeyEqual >

QList< Val > QHash< Key, Val, Hash, KeyEqual >::values ( ) const

Returns a list containing all the values in the hash, in an arbitrary order. If a key is associated multiple values, all of its values will be in the list, and not just the most recently inserted one.

The order is guaranteed to be the same as that used by keys().

See also: keys(), value()

Friends And Related Function Documentation

QDataStream & operator<<	(	QDataStream &	stream,
		const QHash< Key, Val, Hash, KeyEqual > &	hash
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QHash< Key, Val, Hash, KeyEqual > &	hash
	)

Refer to Serializing Data Types for additional information.

uint qHash ( char key )

uint qHash ( const QBitArray & key )

uint qHash ( const QByteArray & key )

uint qHash	(	const QHostAddress &	key,
		uint	seed = `0`
	)

uint qHash	(	const QItemSelectionRange &	key,
		uint	seed = `0`
	)

uint qHash	(	const QList< T > &	key,
		uint	seed = `0`
	)

uint qHash ( const QPair< T1, T2 > & key )

uint qHash	(	const QSharedPointer< T > &	ptr,
		uint	seed = `0`
	)

uint qHash ( const QSourceLocation & location )

uint qHash	(	const QSslError &	key,
		uint	seed
	)

uint qHash ( const QString & key )

uint qHash	(	const QTransform &	key,
		uint	seed = `0`
	)

uint qHash	(	const QUrl &	key,
		uint	seed = `0`
	)

uint qHash	(	const QUrlQuery &	key,
		uint	seed = `0`
	)

uint qHash	(	const QVector< T > &	key,
		uint	seed = `0`
	)

uint qHash ( const QXmlName & name )

uint qHash ( const QXmlNodeModelIndex & index )

The hash is computed on QXmlNodeModelIndex::data(), QXmlNodeModelIndex::additionalData(), and QXmlNodeModelIndex::model(). This means the hash key can be used for node indexes from different node models.

uint qHash ( const T * key )

uint qHash ( int key )

uint qHash ( long key )

uint qHash ( QChar key )

uint qHash ( qint64 key )

uint qHash	(	QSslEllipticCurve	curve,
		uint	seed = `0`
	)

uint qHash ( quint64 key )

uint qHash ( short key )

uint qHash ( signed char key )

uint qHash ( uchar key )

uint qHash ( uint key )

uint qHash ( ulong key )

uint qHash ( ushort key )

Classes

Public Typedefs

Public Methods

Related Functions

Detailed Description

template<typename Key, typename Val, typename Hash, typename KeyEqual> class QHash< Key, Val, Hash, KeyEqual >

Constructors

Accessing Elements

Iterators

Constraints on type T

Comparison Example

Member Typedef Documentation

Constructor & Destructor Documentation

Method Documentation

Friends And Related Function Documentation

template<typename Key, typename Val, typename Hash, typename KeyEqual>
class QHash< Key, Val, Hash, KeyEqual >