内容

• 公共类型
• 公共函数
• 相关非成员
• 详细描述

QMultiHash 类

模板 <typename Key, typename T> 类 QMultiHash

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

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

• 所有成员列表，包括继承成员

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 (const QHash<Key, T> & other )
	QMultiHash (InputIterator begin , InputIterator end )
	QMultiHash (std::initializer_list<std::pair<Key, T> > list )
	QMultiHash ()
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 & defaultKey = Key()) 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 , 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 & defaultValue = T()) 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 )

相关非成员

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> 是一种 Qt 一般 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 的迭代器类 (例如： 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 (int i = 0; i < values.size(); ++i)
    cout << values.at(i) << Qt::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() << Qt::endl;
    ++i;
}
					

QMultiHash's key and value data types must be 可赋值数据类型 。例如，无法存储 QWidget 作为值；取而代之，存储 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

[since 5.10] QMultiHash:: const_key_value_iterator

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.

该 typedef 在 Qt 5.10 引入。

另请参阅 QKeyValueIterator .

[since 5.10] QMultiHash:: key_value_iterator

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.

该 typedef 在 Qt 5.10 引入。

另请参阅 QKeyValueIterator .

成员函数文档编制

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 .

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 .

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

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

[since 5.14] 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 第一 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。

该函数在 Qt 5.14 引入。

[since 5.1] 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.

该函数在 Qt 5.1 引入。

QMultiHash:: QMultiHash ()

构造空哈希。

QMultiHash::iterator QMultiHash:: begin ()

返回 STL 样式迭代器 指向哈希中的首项。

另请参阅 constBegin () 和 end ().

QMultiHash::const_iterator QMultiHash:: begin () const

这是重载函数。

[since 5.0] QMultiHash::const_iterator QMultiHash:: cbegin () const

返回常量 STL 样式迭代器 指向哈希中的首项。

该函数在 Qt 5.0 引入。

另请参阅 begin () 和 cend ().

[since 5.0] 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.

该函数在 Qt 5.0 引入。

另请参阅 cbegin () 和 end ().

void QMultiHash:: clear ()

移除哈希的所有项，并释放它所使用的所有内存。

另请参阅 remove ().

QMultiHash::const_iterator QMultiHash:: constBegin () const

返回常量 STL 样式迭代器 指向哈希中的首项。

另请参阅 begin () 和 constEnd ().

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 ().

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

返回迭代器指向的项具有 key 和 value 在哈希中。

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

[since 5.10] 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。

该函数在 Qt 5.10 引入。

另请参阅 keyValueBegin ().

[since 5.10] 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.

该函数在 Qt 5.10 引入。

另请参阅 constKeyValueBegin ().

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

返回 true 若哈希包含的项具有 key and value ；否则返回 false .

另请参阅 contains().

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().

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 ().

QMultiHash::const_iterator QMultiHash:: end () const

这是重载函数。

[since 5.7] 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 ().

该函数在 Qt 5.7 引入。

[since 5.7] QPair < QMultiHash::const_iterator , QMultiHash::const_iterator > QMultiHash:: equal_range (const Key & key ) const

这是重载函数。

该函数在 Qt 5.7 引入。

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

返回迭代器指向的项具有 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.

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 )

插入新项具有 key 和值 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 ().

Key QMultiHash:: key (const T & value , const Key & defaultKey = Key()) const

Returns the first key mapped to value ，或 defaultKey if the hash contains no item mapped to value .

此函数可能很慢 ( 线性时间 )，因为 QMultiHash 's internal data structure is optimized for fast lookup by key, not by value.

[since 5.6] QMultiHash::key_iterator QMultiHash:: keyBegin () const

返回常量 STL 样式迭代器 指向哈希中的第一个 Key。

该函数在 Qt 5.6 引入。

另请参阅 keyEnd ().

[since 5.6] 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.

该函数在 Qt 5.6 引入。

另请参阅 keyBegin ().

[since 5.10] QMultiHash::key_value_iterator QMultiHash:: keyValueBegin ()

返回 STL 样式迭代器 指向第一哈希条目。

该函数在 Qt 5.10 引入。

另请参阅 keyValueEnd ().

[since 5.10] 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。

该函数在 Qt 5.10 引入。

另请参阅 keyValueEnd ().

[since 5.10] 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.

该函数在 Qt 5.10 引入。

另请参阅 keyValueBegin ().

[since 5.10] 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.

该函数在 Qt 5.10 引入。

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 ().

此函数创建新列表，按 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 , 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 )

插入新项具有 key 和值 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 ().

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

交换哈希 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 ().

[since 5.13] 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.

该函数在 Qt 5.13 引入。

另请参阅 keys () 和 values ().

[since 5.13] 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.

该函数在 Qt 5.13 引入。

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 ().

T QMultiHash:: value (const Key & key , const T & defaultValue = T()) const

这是重载函数。

返回值关联 key .

若哈希包含的项不具有 key ，函数返回 defaultValue , which is a 默认构造值 if the parameter has not been specified.

If there are multiple items for the key in the hash, the value of the most recently inserted one is returned.

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 ().

此函数创建新列表，按 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 )

返回值关联 key 作为可修改引用。

若哈希包含的项不具有 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。

[since 5.8] 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().

该函数在 Qt 5.8 引入。

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

写入哈希 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 )

读取哈希从流 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 .