QMultiHash 类

template <typename Key, typename T> class QMultiHash

QMultiHash 类是方便 QHash 子类,提供多值哈希。 更多...

头: #include <QMultiHash>
CMake: find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake: QT += core

注意: 此类的所有函数 可重入 .

公共类型

class const_iterator
class iterator
class key_iterator
const_key_value_iterator
key_value_iterator

公共函数

QMultiHash ()
QMultiHash (std::initializer_list<std::pair<Key, T>> list )
QMultiHash (InputIterator begin , InputIterator end )
QMultiHash (const QHash<Key, T> & other )
auto asKeyValueRange () &
auto asKeyValueRange () const &
auto asKeyValueRange () &&
auto asKeyValueRange () const &&
QMultiHash::iterator begin ()
QMultiHash::const_iterator begin () const
QMultiHash::const_iterator cbegin () const
QMultiHash::const_iterator cend () const
void clear ()
QMultiHash::const_iterator constBegin () const
QMultiHash::const_iterator constEnd () const
QMultiHash::const_iterator constFind (const Key & key , const T & value ) const
QMultiHash::const_key_value_iterator constKeyValueBegin () const
QMultiHash::const_key_value_iterator constKeyValueEnd () const
bool contains (const Key & key , const T & value ) const
qsizetype count (const Key & key , const T & value ) const
QMultiHash::iterator emplace (const Key & key , Args &&... args )
QMultiHash::iterator emplace (Key && key , Args &&... args )
QMultiHash::iterator emplaceReplace (const Key & key , Args &&... args )
QMultiHash::iterator emplaceReplace (Key && key , Args &&... args )
QMultiHash::iterator end ()
QMultiHash::const_iterator end () const
QPair<QMultiHash::iterator, QMultiHash::iterator> equal_range (const Key & key )
QPair<QMultiHash::const_iterator, QMultiHash::const_iterator> equal_range (const Key & key ) const
QMultiHash::iterator find (const Key & key , const T & value )
QMultiHash::const_iterator find (const Key & key , const T & value ) const
QMultiHash::iterator insert (const Key & key , const T & value )
Key key (const T & value ) const
Key key (const T & value , const Key & defaultKey ) const
QMultiHash::key_iterator keyBegin () const
QMultiHash::key_iterator keyEnd () const
QMultiHash::key_value_iterator keyValueBegin ()
QMultiHash::const_key_value_iterator keyValueBegin () const
QMultiHash::key_value_iterator keyValueEnd ()
QMultiHash::const_key_value_iterator keyValueEnd () const
QList<Key> keys () const
qsizetype remove (const Key & key )
qsizetype remove (const Key & key , const T & value )
qsizetype removeIf (Predicate pred )
QMultiHash::iterator replace (const Key & key , const T & value )
void swap (QMultiHash<Key, T> & other )
T take (const Key & key )
QList<Key> uniqueKeys () const
QMultiHash<Key, T> & unite (const QMultiHash<Key, T> & other )
QMultiHash<Key, T> & unite (const QHash<Key, T> & other )
T value (const Key & key ) const
T value (const Key & key , const T & defaultValue ) const
QList<T> values () const
QList<T> values (const Key & key ) const
QMultiHash<Key, T> operator+ (const QMultiHash<Key, T> & other ) const
QMultiHash<Key, T> & operator+= (const QMultiHash<Key, T> & other )
T & operator[] (const Key & key )
qsizetype erase_if (QMultiHash<Key, T> & hash , Predicate pred )
size_t qHash (const QMultiHash<Key, T> & key , size_t seed = 0)
QDataStream & operator<< (QDataStream & out , const QMultiHash<Key, T> & hash )
QDataStream & operator>> (QDataStream & in , QMultiHash<Key, T> & hash )

详细描述

QMultiHash<Key, T> is one of Qt's generic 容器类 . 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+=().

不像 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.

范例:

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
					

不像 QHash , QMultiHash provides no operator[]. Use value () 或 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 (auto i : std::as_const(values))
    cout << 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:

auto i = hash.constFind("plenty");
while (i != hash.cend() && 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 qHash () function in the type's namespace that returns a hash value for an argument of the key's type. See the QHash 文档编制了解细节。

另请参阅 QHash , QHashIterator , QMutableHashIterator ,和 QMultiMap .

成员类型文档编制

QMultiHash:: const_key_value_iterator

The QMap::const_key_value_iterator typedef provides an STL-style const iterator for QMultiHash and QMultiHash .

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.

另请参阅 QKeyValueIterator .

QMultiHash:: key_value_iterator

The QMap::key_value_iterator typedef provides an STL-style iterator for QMultiHash and QMultiHash .

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.

另请参阅 QKeyValueIterator .

成员函数文档编制

template <typename Args> QMultiHash::iterator QMultiHash:: emplace ( Key && key , Args &&... args )

template <typename Args> QMultiHash::iterator QMultiHash:: emplace (const Key & key , Args &&... args )

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.

另请参阅 insert .

template <typename Args> QMultiHash::iterator QMultiHash:: emplaceReplace ( Key && key , Args &&... args )

template <typename Args> QMultiHash::iterator QMultiHash:: emplaceReplace (const Key & key , Args &&... args )

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.

另请参阅 replace and emplace .

[noexcept] T QMultiHash:: value (const Key & key ) const

[noexcept] T QMultiHash:: value (const Key & key , const T & defaultValue ) const

Returns the value associated with the key .

If the hash contains no item with the key , the function returns defaultValue ,或 默认构造值 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.

[noexcept] Key QMultiHash:: key (const T & value ) const

[noexcept] Key QMultiHash:: key (const T & value , const Key & defaultKey ) const

Returns the first key mapped to value . If the hash contains no item mapped to value ,返回 defaultKey ,或 default-constructed key if this parameter has not been supplied.

This function can be slow ( 线性时间 ),因为 QMultiHash 's internal data structure is optimized for fast lookup by key, not by value.

[since 6.4] auto QMultiHash:: asKeyValueRange () &

[since 6.4] auto QMultiHash:: asKeyValueRange () &&

[since 6.4] auto QMultiHash:: asKeyValueRange () const &

[since 6.4] auto QMultiHash:: asKeyValueRange () const &&

Returns a range object that allows iteration over this hash as key/value pairs. For instance, this range object can be used in a range-based for loop, in combination with a structured binding declaration:

QMultiHash<QString, int> hash;
hash.insert("January", 1);
hash.insert("February", 2);
// ...
hash.insert("December", 12);
for (auto [key, value] : hash.asKeyValueRange()) {
    cout << qPrintable(key) << ": " << value << endl;
    --value; // convert to JS month indexing
}
					

Note that both the key and the value obtained this way are references to the ones in the hash. Specifically, mutating the value will modify the hash itself.

该函数在 Qt 6.4 引入。

另请参阅 QKeyValueIterator .

[noexcept] QMultiHash:: QMultiHash ()

构造空哈希。

QMultiHash:: QMultiHash ( std::initializer_list < std::pair < Key , T >> list )

Constructs a multi-hash with a copy of each of the elements in the initializer list list .

This function is only available if the program is being compiled in C++11 mode.

template <typename InputIterator> QMultiHash:: QMultiHash ( InputIterator begin , InputIterator end )

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 分别。

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

构造副本为 other (which can be a QHash or a QMultiHash).

QMultiHash::iterator QMultiHash:: begin ()

返回 STL 样式迭代器 pointing to the first item in the hash.

另请参阅 constBegin () 和 end ().

[noexcept] QMultiHash::const_iterator QMultiHash:: begin () const

这是重载函数。

[noexcept] QMultiHash::const_iterator QMultiHash:: cbegin () const

返回常量 STL 样式迭代器 pointing to the first item in the hash.

另请参阅 begin () 和 cend ().

[noexcept] QMultiHash::const_iterator QMultiHash:: cend () const

返回常量 STL 样式迭代器 pointing to the imaginary item after the last item in the hash.

另请参阅 cbegin () 和 end ().

[noexcept(...)] void QMultiHash:: clear ()

Removes all items from the hash and frees up all memory used by it.

注意: This function does not throw any exception when "std::is_nothrow_destructible<Node>::value" is true.

另请参阅 remove ().

[noexcept] QMultiHash::const_iterator QMultiHash:: constBegin () const

返回常量 STL 样式迭代器 pointing to the first item in the hash.

另请参阅 begin () 和 constEnd ().

[noexcept] QMultiHash::const_iterator QMultiHash:: constEnd () const

返回常量 STL 样式迭代器 pointing to the imaginary item after the last item in the hash.

另请参阅 constBegin () 和 end ().

[noexcept] QMultiHash::const_iterator QMultiHash:: constFind (const Key & key , const T & value ) const

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

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

[noexcept] QMultiHash::const_key_value_iterator QMultiHash:: constKeyValueBegin () const

返回常量 STL 样式迭代器 指向第一哈希条目。

另请参阅 keyValueBegin ().

[noexcept] QMultiHash::const_key_value_iterator QMultiHash:: constKeyValueEnd () const

返回常量 STL 样式迭代器 pointing to the imaginary entry after the last entry in the hash.

另请参阅 constKeyValueBegin ().

[noexcept] bool QMultiHash:: contains (const Key & key , const T & value ) const

返回 true if the hash contains an item with the key and value ;否则返回 false .

另请参阅 contains().

[noexcept] qsizetype QMultiHash:: count (const Key & key , const T & value ) const

Returns the number of items with the key and value .

另请参阅 count().

[noexcept] QMultiHash::iterator QMultiHash:: end ()

返回 STL 样式迭代器 pointing to the imaginary item after the last item in the hash.

另请参阅 begin () 和 constEnd ().

[noexcept] QMultiHash::const_iterator QMultiHash:: end () const

这是重载函数。

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

Returns a pair of iterators delimiting the range of values [first, second) , that are stored under key . If the range is empty then both iterators will be equal to end ().

[noexcept] QPair < QMultiHash::const_iterator , QMultiHash::const_iterator > QMultiHash:: equal_range (const Key & key ) const

这是重载函数。

QMultiHash::iterator QMultiHash:: find (const Key & key , const T & value )

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.

[noexcept] QMultiHash::const_iterator QMultiHash:: find (const Key & key , const T & value ) const

这是重载函数。

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

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.)

另请参阅 replace ().

[noexcept] QMultiHash::key_iterator QMultiHash:: keyBegin () const

返回常量 STL 样式迭代器 pointing to the first key in the hash.

另请参阅 keyEnd ().

[noexcept] QMultiHash::key_iterator QMultiHash:: keyEnd () const

返回常量 STL 样式迭代器 pointing to the imaginary item after the last key in the hash.

另请参阅 keyBegin ().

[noexcept] QMultiHash::key_value_iterator QMultiHash:: keyValueBegin ()

返回 STL 样式迭代器 指向第一哈希条目。

另请参阅 keyValueEnd ().

[noexcept] QMultiHash::const_key_value_iterator QMultiHash:: keyValueBegin () const

返回常量 STL 样式迭代器 指向第一哈希条目。

另请参阅 keyValueEnd ().

[noexcept] QMultiHash::key_value_iterator QMultiHash:: keyValueEnd ()

返回 STL 样式迭代器 pointing to the imaginary entry after the last entry in the hash.

另请参阅 keyValueBegin ().

[noexcept] QMultiHash::const_key_value_iterator QMultiHash:: keyValueEnd () const

返回常量 STL 样式迭代器 pointing to the imaginary entry after the last entry in the hash.

另请参阅 keyValueBegin ().

QList < Key > QMultiHash:: keys () const

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 线性时间 . The time and memory use that entails can be avoided by iterating from keyBegin () 到 keyEnd ().

另请参阅 values () 和 key ().

qsizetype QMultiHash:: remove (const Key & key )

Removes all the items that have the key from the hash. Returns the number of items removed.

另请参阅 remove().

qsizetype QMultiHash:: remove (const Key & key , const T & value )

Removes all the items that have the key and the value value from the hash. Returns the number of items removed.

另请参阅 remove ().

[since 6.1] template <typename Predicate> qsizetype QMultiHash:: removeIf ( Predicate pred )

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.

该函数在 Qt 6.1 引入。

另请参阅 clear () 和 take ().

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

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 .

另请参阅 insert ().

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

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

T QMultiHash:: take (const Key & key )

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 默认构造值 . If there are multiple items for key in the hash, only the most recently inserted one is removed.

若不使用返回值, remove () 效率更高。

另请参阅 remove ().

QList < Key > QMultiHash:: uniqueKeys () const

Returns a list containing all the keys in the map. Keys that occur multiple times in the map occur only once in the returned list.

另请参阅 keys () 和 values ().

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

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

另请参阅 insert ().

[since 6.0] QMultiHash < Key , T > &QMultiHash:: unite (const QHash < Key , T > & other )

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

该函数在 Qt 6.0 引入。

另请参阅 insert ().

QList < T > QMultiHash:: values () const

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 线性时间 . The time and memory use that entails can be avoided by iterating from keyValueBegin () 到 keyValueEnd ().

另请参阅 keys () 和 value ().

QList < T > QMultiHash:: values (const Key & key ) const

这是重载函数。

Returns a list of all the values associated with the key , from the most recently inserted to the least recently inserted.

另请参阅 count () 和 insert ().

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

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.

另请参阅 operator+= ().

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

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

另请参阅 unite () 和 insert ().

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

Returns the value associated with the key as a modifiable reference.

If the hash contains no item with the key , the function inserts a 默认构造值 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.

另请参阅 insert () 和 value ().

相关非成员

[since 6.1] template <typename Key, typename T, typename Predicate> qsizetype erase_if ( QMultiHash < Key , T > & hash , Predicate pred )

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.

该函数在 Qt 6.1 引入。

[noexcept(...)] template <typename Key, typename T> size_t qHash (const QMultiHash < Key , T > & key , size_t seed = 0)

返回哈希值为 key ,使用 seed 做计算种子。

类型 T must be supported by qHash().

注意: This function does not throw any exception when "noexcept(qHash(std::declval<Key&>())) && noexcept(qHash(std::declval<T&>()))" is true.

template <typename Key, typename T> QDataStream & operator<< ( QDataStream & out , const QMultiHash < Key , T > & hash )

Writes the hash hash 到流 out .

This function requires the key and value types to implement operator<<() .

另请参阅 序列化 Qt 数据类型 .

template <typename Key, typename T> QDataStream & operator>> ( QDataStream & in , QMultiHash < Key , T > & hash )

Reads a hash from stream in into hash .

This function requires the key and value types to implement operator>>() .

另请参阅 序列化 Qt 数据类型 .