The QMultiHash class is a convenience QHash subclass that provides multi-valued hashes. More...
#include <qhash.h>
Classes | |
| class | const_iterator |
| The QMultiHash::const_iterator class provides an STL-style const iterator for QMultiHash. More... | |
| class | iterator |
| The QMultiHash::iterator class provides an STL-style non-const iterator for QMultiHash. More... | |
| class | key_iterator |
| The QMultiHash::key_iterator class provides an STL-style const iterator for QMultiHash keys. More... | |
Public Types | |
| using | key_type = Key |
| using | mapped_type = T |
| using | value_type = T |
| using | size_type = qsizetype |
| using | difference_type = qsizetype |
| using | reference = T & |
| using | const_reference = const T & |
| typedef QKeyValueIterator< const Key &, const T &, const_iterator > | const_key_value_iterator |
| The QMap::const_key_value_iterator typedef provides an STL-style const iterator for QMultiHash and QMultiHash. More... | |
| typedef QKeyValueIterator< const Key &, T &, iterator > | key_value_iterator |
| The QMap::key_value_iterator typedef provides an STL-style iterator for QMultiHash and QMultiHash. More... | |
| typedef iterator | Iterator |
| typedef const_iterator | ConstIterator |
Static Public Member Functions | |
| static float | max_load_factor () noexcept |
| static size_t | max_bucket_count () noexcept |
Friends | |
| class | iterator |
| class | const_iterator |
Related Functions | |
(Note that these are not member functions.) | |
| template< class Key, class T > QDataStream & | operator<< (QDataStream &out, const QMultiHash< Key, T > &hash) |
| template< class Key, class T > QDataStream & | operator>> (QDataStream &in, QMultiHash< Key, T > &hash) |
| template< class Key, class T > size_t | qHash (const QMultiHash< Key, T > &key, size_t seed=0) |
| template< typename Key, typename T, typename Predicate > qsizetype | erase_if (QMultiHash< Key, T > &hash, Predicate pred) |
Detailed Description
template<typename Key, typename T>
class QMultiHash< Key, T >
The QMultiHash class is a convenience QHash subclass that provides multi-valued hashes.
\inmodule QtCore
\reentrant
QMultiHash<Key, T> is one of Qt's generic \l{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.
QMultiHash mostly mirrors QHash's API. 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 opposed to QHash, it provides an insert() function that allows the insertion of multiple items with the same key. The replace() function corresponds to QHash::insert(). It also provides convenient operator+() and operator+=().
Unlike QMultiMap, QMultiHash does not provide and ordering of the inserted items. The only guarantee is that items that share the same key will appear consecutively, from the most recently to the least recently inserted value.
Example:
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>:
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's key and value data types must be \l{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 qHash() function in the type's namespace that returns a hash value for an argument of the key's type. See the QHash documentation for details.
Member Typedef Documentation
◆ const_key_value_iterator
| QMultiHash< Key, T >::const_key_value_iterator |
The QMap::const_key_value_iterator typedef provides an STL-style const iterator for QMultiHash and QMultiHash.
\inmodule QtCore
- Since
- 5.10
QMultiHash::const_key_value_iterator is essentially the same as QMultiHash::const_iterator with the difference that operator*() returns a key/value pair instead of a value.
- See also
- QKeyValueIterator
◆ const_reference
| using QMultiHash< Key, T >::const_reference = const T & |
◆ ConstIterator
| typedef const_iterator QMultiHash< Key, T >::ConstIterator |
◆ difference_type
| using QMultiHash< Key, T >::difference_type = qsizetype |
◆ Iterator
| typedef iterator QMultiHash< Key, T >::Iterator |
◆ key_type
| using QMultiHash< Key, T >::key_type = Key |
◆ key_value_iterator
| QMultiHash< Key, T >::key_value_iterator |
The QMap::key_value_iterator typedef provides an STL-style iterator for QMultiHash and QMultiHash.
\inmodule QtCore
- Since
- 5.10
QMultiHash::key_value_iterator is essentially the same as QMultiHash::iterator with the difference that operator*() returns a key/value pair instead of a value.
- See also
- QKeyValueIterator
◆ mapped_type
| using QMultiHash< Key, T >::mapped_type = T |
◆ reference
| using QMultiHash< Key, T >::reference = T & |
◆ size_type
| using QMultiHash< Key, T >::size_type = qsizetype |
◆ value_type
| using QMultiHash< Key, T >::value_type = T |
Constructor & Destructor Documentation
◆ QMultiHash() [1/8]
|
defaultnoexcept |
Constructs an empty hash.
◆ QMultiHash() [2/8]
|
inline |
◆ QMultiHash() [3/8]
|
inline |
- Since
- 5.14
Constructs a multi-hash with a copy of each of the elements in the iterator range [begin, end). Either the elements iterated by the range must be objects with {first} and {second} data members (like {QPair}, {std::pair}, etc.) convertible to Key and to T respectively; or the iterators must have {key()} and {value()} member functions, returning a key convertible to Key and a value convertible to T respectively.
Definition at line 1322 of file qhash.h.
◆ QMultiHash() [4/8]
|
inline |
◆ QMultiHash() [5/8]
|
inlinenoexcept |
◆ ~QMultiHash()
|
inline |
◆ QMultiHash() [6/8]
|
inlinenoexcept |
◆ QMultiHash() [7/8]
|
inlineexplicit |
Constructs a copy of other (which can be a QHash or a QMultiHash).
◆ QMultiHash() [8/8]
|
inlineexplicit |
Member Function Documentation
◆ begin() [1/2]
|
inline |
Returns an \l{STL-style iterators}{STL-style iterator} pointing to the first item in the hash.
- See also
- constBegin(), end()
Definition at line 1767 of file qhash.h.
◆ begin() [2/2]
|
inlinenoexcept |
◆ bucket_count()
|
inlinenoexcept |
◆ capacity()
|
inlinenoexcept |
◆ cbegin()
|
inlinenoexcept |
◆ cend()
|
inlinenoexcept |
◆ clear()
|
inlinenoexcept |
◆ constBegin()
|
inlinenoexcept |
Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first item in the hash.
- See also
- begin(), constEnd()
Definition at line 1770 of file qhash.h.
◆ constEnd()
|
inlinenoexcept |
Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary item after the last item in the hash.
- See also
- constBegin(), end()
Definition at line 1774 of file qhash.h.
◆ constFind() [1/2]
|
inlinenoexcept |
◆ constFind() [2/2]
|
inlinenoexcept |
- Since
- 4.3
Returns an iterator pointing to the item with the key and the value in the hash.
If the hash contains no such item, the function returns constEnd().
Definition at line 2011 of file qhash.h.
◆ constKeyValueBegin()
|
inlinenoexcept |
- Since
- 5.10
Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first entry in the hash.
- See also
- keyValueBegin()
Definition at line 1780 of file qhash.h.
◆ constKeyValueEnd()
|
inlinenoexcept |
- Since
- 5.10
Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary entry after the last entry in the hash.
- See also
- constKeyValueBegin()
Definition at line 1782 of file qhash.h.
◆ contains() [1/2]
|
inlinenoexcept |
◆ contains() [2/2]
|
inlinenoexcept |
- Since
- 4.3
Returns true if the hash contains an item with the key and value; otherwise returns false.
- See also
- contains()
Definition at line 1924 of file qhash.h.
◆ count() [1/3]
|
inlinenoexcept |
◆ count() [2/3]
|
inlinenoexcept |
◆ count() [3/3]
◆ detach() [1/2]
|
inline |
◆ detach() [2/2]
|
inline |
◆ emplace() [1/2]
|
inline |
◆ emplace() [2/2]
|
inline |
Inserts a new element into the container. This new element is constructed in-place using args as the arguments for its construction.
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.)
Returns an iterator pointing to the new element.
- See also
- insert
Definition at line 1873 of file qhash.h.
◆ emplaceReplace() [1/2]
|
inline |
◆ emplaceReplace() [2/2]
|
inline |
Inserts a new element into the container. This new element is constructed in-place using args as the arguments for its construction.
If there is already an item with the same key in the hash, that item's value is replaced with a value constructed from args.
Returns an iterator pointing to the new element.
Definition at line 1906 of file qhash.h.
◆ empty()
|
inlinenoexcept |
◆ end() [1/2]
|
inlinenoexcept |
◆ end() [2/2]
|
inlinenoexcept |
Returns an \l{STL-style iterators}{STL-style iterator} pointing to the imaginary item after the last item in the hash.
- See also
- begin(), constEnd()
Definition at line 1771 of file qhash.h.
◆ equal_range() [1/2]
◆ equal_range() [2/2]
|
inlinenoexcept |
◆ erase()
|
inline |
◆ find() [1/4]
|
inline |
◆ find() [2/4]
|
inlinenoexcept |
◆ find() [3/4]
|
inline |
- Since
- 4.3
Returns an iterator pointing to the item with the key and value. 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.
Definition at line 1998 of file qhash.h.
◆ find() [4/4]
|
inlinenoexcept |
◆ insert()
|
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 1861 of file qhash.h.
◆ isDetached()
|
inlinenoexcept |
◆ isEmpty()
|
inlinenoexcept |
◆ isSharedWith()
|
inlinenoexcept |
◆ key() [1/2]
◆ key() [2/2]
|
inlinenoexcept |
- Since
- 4.3
Returns the first key mapped to value. If the hash contains no item mapped to value, returns defaultKey, or a \l{default-constructed value}{default-constructed key} if this parameter has not been supplied.
This function can be slow (\l{linear time}), because QMultiHash's internal data structure is optimized for fast lookup by key, not by value.
◆ keyBegin()
|
inlinenoexcept |
◆ keyEnd()
|
inlinenoexcept |
- Since
- 5.6
Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary item after the last key in the hash.
- See also
- keyBegin()
Definition at line 1776 of file qhash.h.
◆ keys() [1/2]
|
inline |
Returns a list containing all the keys in the hash, in an arbitrary order. Keys that occur multiple times in the hash also occur multiple times in the list.
The order is guaranteed to be the same as that used by values().
This function creates a new list, in \l {linear time}. The time and memory use that entails can be avoided by iterating from \l keyBegin() to \l keyEnd().
Definition at line 1605 of file qhash.h.
◆ keys() [2/2]
|
inline |
◆ keyValueBegin() [1/2]
|
inlinenoexcept |
- Since
- 5.10
Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first entry in the hash.
- See also
- keyValueEnd()
Definition at line 1779 of file qhash.h.
◆ keyValueBegin() [2/2]
|
inlinenoexcept |
- Since
- 5.10
Returns an \l{STL-style iterators}{STL-style iterator} pointing to the first entry in the hash.
- See also
- keyValueEnd()
Definition at line 1777 of file qhash.h.
◆ keyValueEnd() [1/2]
|
inlinenoexcept |
- Since
- 5.10
Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary entry after the last entry in the hash.
- See also
- keyValueBegin()
Definition at line 1781 of file qhash.h.
◆ keyValueEnd() [2/2]
|
inlinenoexcept |
- Since
- 5.10
Returns an \l{STL-style iterators}{STL-style iterator} pointing to the imaginary entry after the last entry in the hash.
- See also
- keyValueBegin()
Definition at line 1778 of file qhash.h.
◆ load_factor()
|
inlinenoexcept |
◆ max_bucket_count()
|
inlinestaticnoexcept |
◆ max_load_factor()
|
inlinestaticnoexcept |
◆ operator!=()
|
inlinenoexcept |
◆ operator+()
|
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 1921 of file qhash.h.
◆ operator+=()
|
inline |
◆ operator=() [1/2]
|
inlinenoexcept |
◆ operator=() [2/2]
|
inlinenoexcept |
◆ operator==()
|
inlinenoexcept |
◆ operator[]() [1/2]
|
inline |
Returns the value associated with the key as a modifiable reference.
If the hash contains no item with the key, the function inserts a \l{default-constructed value} into the hash with the key, and returns a reference to it.
If the hash contains multiple items with the key, this function returns a reference to the most recently inserted value.
◆ operator[]() [2/2]
|
inlinenoexcept |
◆ remove() [1/2]
|
inline |
◆ remove() [2/2]
◆ removeIf()
|
inline |
- Since
- 6.1
Removes all elements for which the predicate pred returns true from the multi hash.
The function supports predicates which take either an argument of type {QMultiHash<Key, T>::iterator}, or an argument of type {std::pair<const Key &, T &>}.
Returns the number of elements removed, if any.
Definition at line 1481 of file qhash.h.
◆ replace()
|
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 1894 of file qhash.h.
◆ reserve()
|
inline |
◆ size()
|
inlinenoexcept |
◆ squeeze()
|
inline |
◆ swap()
|
inlinenoexcept |
◆ take()
|
inline |
Removes the item with the key from the hash and returns the value associated with it.
If the item does not exist in the hash, the function simply returns a \l{default-constructed value}. If there are multiple items for key in the hash, only the most recently inserted one is removed.
If you don't use the return value, remove() is more efficient.
- See also
- remove()
Definition at line 1485 of file qhash.h.
◆ uniqueKeys()
|
inline |
◆ unite() [1/3]
|
inline |
◆ unite() [2/3]
|
inline |
◆ unite() [3/3]
|
inline |
◆ value() [1/2]
◆ value() [2/2]
|
inlinenoexcept |
Returns the value associated with the key.
If the hash contains no item with the key, the function returns defaultValue, or a \l{default-constructed value} if this parameter has not been supplied.
If there are multiple items for the key in the hash, the value of the most recently inserted one is returned.
Definition at line 1568 of file qhash.h.
◆ values() [1/2]
|
inline |
Returns a list containing all the values in the hash, in an arbitrary order. If a key is associated with 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().
This function creates a new list, in \l {linear time}. The time and memory use that entails can be avoided by iterating from \l keyValueBegin() to \l keyValueEnd().
Definition at line 1617 of file qhash.h.
◆ values() [2/2]
|
inline |
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Returns a list of all the values associated with the key, from the most recently inserted to the least recently inserted.
Definition at line 1618 of file qhash.h.
Friends And Related Function Documentation
◆ const_iterator
|
friend |
◆ erase_if()
|
related |
- Since
- 6.1
Removes all elements for which the predicate pred returns true from the multi hash hash.
The function supports predicates which take either an argument of type {QMultiHash<Key, T>::iterator}, or an argument of type {std::pair<const Key &, T &>}.
Returns the number of elements removed, if any.
Definition at line 2158 of file qhash.h.
◆ iterator
|
friend |
◆ operator<<()
|
related |
Writes the hash hash to stream out.
This function requires the key and value types to implement operator<<().
Definition at line 481 of file qdatastream.h.
◆ operator>>()
|
related |
Reads a hash from stream in into hash.
This function requires the key and value types to implement operator>>().
Definition at line 481 of file qdatastream.h.
◆ qHash()
|
related |
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
