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QMultiMap 类

模板 <typename Key, typename T> 类 QMultiMap

QMultiMap 类是提供具有多个等效键的关联数组的模板类。 更多...

头： #include <QMultiMap>
CMake: find_package(Qt6 COMPONENTS Core REQUIRED)
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
  ConstIterator
  Iterator
  const_key_value_iterator
  difference_type
  key_type
  key_value_iterator
  mapped_type
  size_type

公共函数

  QMultiMap (const QMultiMap<Key, T> & other )
  QMultiMap (QMultiMap<Key, T> && other )
  QMultiMap (std::multimap<Key, T> && other )
  QMultiMap (const std::multimap<Key, T> & other )
  QMultiMap (QMap<Key, T> && other )
  QMultiMap (const QMap<Key, T> & other )
  QMultiMap (std::initializer_list<std::pair<Key, T> > list )
  QMultiMap ()
QMultiMap<Key, T> & operator= (QMultiMap<Key, T> && other )
QMultiMap<Key, T> & operator= (const QMultiMap<Key, T> & other )
  ~QMultiMap ()
QMultiMap::iterator begin ()
QMultiMap::const_iterator begin () const
QMultiMap::const_iterator cbegin () const
QMultiMap::const_iterator cend () const
void clear ()
QMultiMap::const_iterator constBegin () const
QMultiMap::const_iterator constEnd () const
QMultiMap::const_iterator constFind (const Key & key ) const
QMultiMap::const_iterator constFind (const Key & key , const T & value ) const
QMultiMap::const_key_value_iterator constKeyValueBegin () const
QMultiMap::const_key_value_iterator constKeyValueEnd () const
bool contains (const Key & key ) const
bool contains (const Key & key , const T & value ) const
QMultiMap::size_type count (const Key & key ) const
QMultiMap::size_type count (const Key & key , const T & value ) const
QMultiMap::size_type count () const
bool empty () const
QMultiMap::iterator end ()
QMultiMap::const_iterator end () const
QPair<QMultiMap::iterator, QMultiMap::iterator> equal_range (const Key & key )
QPair<QMultiMap::const_iterator, QMultiMap::const_iterator> equal_range (const Key & key ) const
QMultiMap::iterator erase (QMultiMap::const_iterator pos )
QMultiMap::iterator erase (QMultiMap::const_iterator first , QMultiMap::const_iterator last )
QMultiMap::iterator find (const Key & key )
QMultiMap::const_iterator find (const Key & key ) const
QMultiMap::const_iterator find (const Key & key , const T & value ) const
T & first ()
const T & first () const
const Key & firstKey () const
QMultiMap::iterator insert (const Key & key , const T & value )
QMultiMap::iterator insert (QMultiMap::const_iterator pos , const Key & key , const T & value )
bool isEmpty () const
Key key (const T & value , const Key & defaultKey = Key()) const
QMultiMap::key_iterator keyBegin () const
QMultiMap::key_iterator keyEnd () const
QMultiMap::key_value_iterator keyValueBegin ()
QMultiMap::const_key_value_iterator keyValueBegin () const
QMultiMap::key_value_iterator keyValueEnd ()
QMultiMap::const_key_value_iterator keyValueEnd () const
QList<Key> keys () const
QList<Key> keys (const T & value ) const
T & last ()
const T & last () const
const Key & lastKey () const
QMultiMap::iterator lowerBound (const Key & key )
QMultiMap::const_iterator lowerBound (const Key & key ) const
QMultiMap::size_type remove (const Key & key )
QMultiMap::size_type remove (const Key & key , const T & value )
QMultiMap::size_type removeIf (Predicate pred )
QMultiMap::iterator replace (const Key & key , const T & value )
QMultiMap::size_type size () const
void swap (QMultiMap<Key, T> & other )
T take (const Key & key )
std::multimap<Key, T> toStdMultiMap () const &
QList<Key> uniqueKeys () const
QMultiMap<Key, T> & unite (const QMultiMap<Key, T> & other )
QMultiMap<Key, T> & unite (QMultiMap<Key, T> && other )
QMultiMap::iterator upperBound (const Key & key )
QMultiMap::const_iterator upperBound (const Key & key ) const
T value (const Key & key , const T & defaultValue = T()) const
QList<T> values () const
QList<T> values (const Key & key ) const
qsizetype erase_if (QMultiMap<Key, T> & map , Predicate pred )
bool operator!= (const QMultiMap<Key, T> & lhs , const QMultiMap<Key, T> & rhs )
QDataStream & operator<< (QDataStream & out , const QMultiMap<Key, T> & map )
bool operator== (const QMultiMap<Key, T> & lhs , const QMultiMap<Key, T> & rhs )
QDataStream & operator>> (QDataStream & in , QMultiMap<Key, T> & map )

详细描述

QMultiMap<Key, T> 是一种 Qt 一般 容器类 。它存储 (key, value) 对，并提供按 Key 的快速查找。

QMultiMap 和 QMultiHash 提供非常类似的功能。差异是：

  • QMultiHash 提供比 QMultiMap 平均更快的查找 (见 算法的复杂性 了解细节。)
  • 当遍历 QMultiHash ，项是任意排序的。采用 QMultiMap，项始终按 Key 排序。
  • Key 类型对于 QMultiHash 必须提供 operator==() 和全局 qHash (Key) function. The key type of a QMultiMap must provide operator<() specifying a total order. Since Qt 5.8.1 it is also safe to use a pointer type as key, even if the underlying operator<() does not provide a total order.

这里是 QMultiMap 范例具有 QString 键和 int 值： 

QMultiMap<QString, int> multimap;

To insert a (key, value) pair into the multi map, you can use insert (): 

multimap.insert("a", 1);
multimap.insert("b", 3);
multimap.insert("c", 7);
multimap.insert("c", -5);

This inserts the following three (key, value) pairs into the QMultiMap: ("a", 1), ("b", 3), ("c", 7), and ("c", -5); note that duplicate keys are allowed.

要查找值，使用 find () 或 value (): 

int num2 = multimap.value("a"); // 1
int num3 = multimap.value("thirteen"); // not found; 0
int num3 = 0;
auto it = multimap.value("b");
if (it != multimap.end()) {
    num3 = it.value();
}

If there is no item with the specified key in the map, these functions return a 默认构造值 .

If you want to check whether the map contains a certain key, use contains (): 

int timeout = 30;
if (multimap.contains("TIMEOUT"))
    timeout = multimap.value("TIMEOUT");
// better:
auto it = multimap.find("TIMEOUT");
if (it != multimap.end())
    timeout = it.value();

There is also a value () overload that uses its second argument as a default value if there is no item with the specified key: 

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

If you want to navigate through all the (key, value) pairs stored in a QMultiMap, you can use an iterator. QMultiMap provides both Java 风格迭代器 ( QMultiMapIterator and QMutableMultiMapIterator ) 和 STL 样式迭代器 ( QMultiMap::const_iterator and QMultiMap::iterator ). Here's how to iterate over a QMultiMap< QString , int> using a Java-style iterator: 

QMultiMapIterator<QString, int> i(multimap);
while (i.hasNext()) {
    i.next();
    cout << i.key() << ": " << i.value() << Qt::endl;
}

Here's the same code, but using an STL-style iterator this time: 

auto i = multimap.constBegin();
while (i != multimap.constEnd()) {
    cout << i.key() << ": " << i.value() << Qt::endl;
    ++i;
}

The items are traversed in ascending key order.

A QMultiMap allows multiple values per key. If you call insert () with a key that already exists in the map, a new (key, value) pair will be inserted. For example: 

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

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 = multimap.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. Another approach is to call find () to get the STL-style iterator for the first item with a key and iterate from there: 

QMultiMap<QString, int>::iterator i = multimap.find("plenty");
while (i != map.end() && i.key() == "plenty") {
    cout << i.value() << Qt::endl;
    ++i;
}
// better:
auto [i, end] = multimap.equal_range("plenty");
while (i != end) {
    cout << i.value() << Qt::endl;
    ++i;
}

If you only need to extract the values from a map (not the keys), you can also use foreach : 

QMap<QString, int> multimap;
...
foreach (int value, multimap)
    cout << value << Qt::endl;

Items can be removed from the multi map in several ways. One way is to call remove (); this will remove any item with the given key. Another way is to use QMutableMultiMapIterator::remove (). In addition, you can clear the entire map using clear ().

It is possible to merge two multi maps by calling unite (), by using operator+(), and by using operator+=(). Example: 

QMultiMap<QString, int> map1, map2, map3;
map1.insert("plenty", 100);
map1.insert("plenty", 2000);
// map1.size() == 2
map2.insert("plenty", 5000);
// map2.size() == 1
map3 = map1 + map2;
// map3.size() == 3

QMultiMap's key and value data types must be 可赋值数据类型 . This covers most data types you are likely to encounter, but the compiler won't let you, for example, store a QWidget 作为值；取而代之，存储 QWidget *. In addition, QMultiMap's key type must provide operator<(). QMap uses it to keep its items sorted, and assumes that two keys x and y are equal if neither x < y nor y < x 为 true。

范例： 

#ifndef EMPLOYEE_H
#define EMPLOYEE_H
class Employee
{
public:
    Employee() {}
    Employee(const QString &name, QDate dateOfBirth);
    ...
private:
    QString myName;
    QDate myDateOfBirth;
};
inline bool operator<(const Employee &e1, const Employee &e2)
{
    if (e1.name() != e2.name())
        return e1.name() < e2.name();
    return e1.dateOfBirth() < e2.dateOfBirth();
}
#endif // EMPLOYEE_H

In the example, we start by comparing the employees' names. If they're equal, we compare their dates of birth to break the tie.

另请参阅 QMultiMapIterator , QMutableMultiMapIterator ，和 QMultiHash .

成员类型文档编制

QMultiMap:: ConstIterator

Qt 样式同义词 QMultiMap <Key, T>::const_iterator.

QMultiMap:: Iterator

Qt 样式同义词 QMultiMap <Key, T>::iterator.

[since 5.10] QMultiMap:: const_key_value_iterator

The QMultiMap::const_key_value_iterator typedef provides an STL-style iterator for QMultiMap .

QMultiMap::const_key_value_iterator is essentially the same as QMultiMap::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 .

[alias] QMultiMap:: difference_type

typedef 对于 ptrdiff_t。为兼容 STL 提供。

[alias] QMultiMap:: key_type

typedef 对于 Key。为兼容 STL 提供。

[since 5.10] QMultiMap:: key_value_iterator

The QMultiMap::key_value_iterator typedef provides an STL-style iterator for QMultiMap .

QMultiMap::key_value_iterator is essentially the same as QMultiMap::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 .

[alias] QMultiMap:: mapped_type

typedef 对于 T。为兼容 STL 提供。

[alias] QMultiMap:: size_type

typedef 对于 int。为兼容 STL 提供。

成员函数文档编制

[default] QMultiMap:: QMultiMap (const QMultiMap < Key , T > & other )

构造副本为 other .

This operation occurs in 常量时间 , because QMultiMap is 隐式共享 . This makes returning a QMultiMap from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and this takes 线性时间 .

另请参阅 operator= ().

[default, since 5.2] QMultiMap:: QMultiMap ( QMultiMap < Key , T > && other )

Move-constructs a QMultiMap instance, making it point at the same object that other 所指向的。

该函数在 Qt 5.2 引入。

QMultiMap:: QMultiMap ( std::multimap < Key , T > && other )

Constructs a multi map by moving from other .

另请参阅 toStdMultiMap ().

QMultiMap:: QMultiMap (const std::multimap < Key , T > & other )

构造副本为 other .

另请参阅 toStdMultiMap ().

[since 6.0] QMultiMap:: QMultiMap ( QMap < Key , T > && other )

若 other is shared, constructs a multi map as a copy of other . Otherwise, constructs a multi map by moving the elements from other .

该函数在 Qt 6.0 引入。

[since 6.0] QMultiMap:: QMultiMap (const QMap < Key , T > & other )

Constructs a multi map as a copy of other .

该函数在 Qt 6.0 引入。

[since 5.1] QMultiMap:: QMultiMap ( std::initializer_list < std::pair < Key , T > > list )

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

该函数在 Qt 5.1 引入。

QMultiMap:: QMultiMap ()

Constructs an empty multi map.

另请参阅 clear ().

[default, since 5.2] QMultiMap < Key , T > &QMultiMap:: operator= ( QMultiMap < Key , T > && other )

移动赋值 other 到此 QMultiMap 实例。

该函数在 Qt 5.2 引入。

[default] QMultiMap < Key , T > &QMultiMap:: operator= (const QMultiMap < Key , T > & other )

赋值 other to this multi map and returns a reference to this multi map.

[default] QMultiMap:: ~QMultiMap ()

Destroys the multi map. References to the values in the multi map, and all iterators over this multi map, become invalid.

QMultiMap::iterator QMultiMap:: begin ()

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

另请参阅 constBegin () 和 end ().

QMultiMap::const_iterator QMultiMap:: begin () const

这是重载函数。

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

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

该函数在 Qt 5.0 引入。

另请参阅 begin () 和 cend ().

[since 5.0] QMultiMap::const_iterator QMultiMap:: cend () const

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

该函数在 Qt 5.0 引入。

另请参阅 cbegin () 和 end ().

void QMultiMap:: clear ()

Removes all items from the multi map.

另请参阅 remove ().

QMultiMap::const_iterator QMultiMap:: constBegin () const

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

另请参阅 begin () 和 constEnd ().

QMultiMap::const_iterator QMultiMap:: constEnd () const

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

另请参阅 constBegin () 和 end ().

QMultiMap::const_iterator QMultiMap:: constFind (const Key & key ) const

Returns an const iterator pointing to the item with key key in the multi map.

If the multi map contains no item with key key ，函数返回 constEnd ().

另请参阅 find () and QMultiMap::constFind().

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

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

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

另请参阅 QMap::constFind ().

[since 5.10] QMultiMap::const_key_value_iterator QMultiMap:: constKeyValueBegin () const

返回常量 STL 样式迭代器 pointing to the first entry in the multi map.

该函数在 Qt 5.10 引入。

另请参阅 keyValueBegin ().

[since 5.10] QMultiMap::const_key_value_iterator QMultiMap:: constKeyValueEnd () const

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

该函数在 Qt 5.10 引入。

另请参阅 constKeyValueBegin ().

bool QMultiMap:: contains (const Key & key ) const

返回 true if the multi map contains an item with key key ；否则返回 false .

另请参阅 count ().

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

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

另请参阅 count ().

QMultiMap::size_type QMultiMap:: count (const Key & key ) const

Returns the number of items associated with key key .

另请参阅 contains () 和 QMultiMap::count ().

QMultiMap::size_type QMultiMap:: count (const Key & key , const T & value ) const

Returns the number of items with key key and value value .

另请参阅 contains () 和 QMultiMap::count ().

QMultiMap::size_type QMultiMap:: count () const

这是重载函数。

如同 size ().

bool QMultiMap:: empty () const

此函数为兼容 STL (标准模板库) 提供。它相当于 isEmpty (), returning true if the map is empty; otherwise returning false.

QMultiMap::iterator QMultiMap:: end ()

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

另请参阅 begin () 和 constEnd ().

QMultiMap::const_iterator QMultiMap:: end () const

这是重载函数。

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

Returns a pair of iterators delimiting the range of values [first, second) , that are stored under key .

[since 5.6] QPair < QMultiMap::const_iterator , QMultiMap::const_iterator > QMultiMap:: equal_range (const Key & key ) const

这是重载函数。

该函数在 Qt 5.6 引入。

QMultiMap::iterator QMultiMap:: erase ( QMultiMap::const_iterator pos )

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

注意： The iterator pos must be valid and dereferenceable.

另请参阅 remove ().

[since 6.0] QMultiMap::iterator QMultiMap:: erase ( QMultiMap::const_iterator first , QMultiMap::const_iterator last )

Removes the (key, value) pairs pointed to by the iterator range [ first , last ) from the multi map. Returns an iterator to the item in the multi map following the last removed element.

注意： 范围 [first, last) must be a valid range in *this .

该函数在 Qt 6.0 引入。

另请参阅 remove ().

QMultiMap::iterator QMultiMap:: find (const Key & key )

Returns an iterator pointing to the item with key key in the multi map.

If the multi map contains no item with key key ，函数返回 end ().

If the map contains multiple items with key key , this function returns an iterator that points to the most recently inserted value. The other values are accessible by incrementing the iterator. For example, here's some code that iterates over all the items with the same key: 

QMultiMap<QString, int>::iterator i = multimap.find("plenty");
while (i != map.end() && i.key() == "plenty") {
    cout << i.value() << Qt::endl;
    ++i;
}
// better:
auto [i, end] = multimap.equal_range("plenty");
while (i != end) {
    cout << i.value() << Qt::endl;
    ++i;
}

另请参阅 constFind (), value (), values (), lowerBound ()，和 upperBound ().

QMultiMap::const_iterator QMultiMap:: find (const Key & key ) const

这是重载函数。

QMultiMap::const_iterator QMultiMap:: find (const Key & key , const T & value ) const

这是重载函数。

Returns a const iterator pointing to the item with the given key and value in the map.

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

If the map contains multiple items with the specified key , this function returns a const iterator that points to the most recently inserted value.

[since 5.2] T &QMultiMap:: first ()

Returns a reference to the first value in the multi map, that is the value mapped to the smallest key. This function assumes that the multi map is not empty.

When unshared (or const version is called), this executes in 常量时间 .

该函数在 Qt 5.2 引入。

另请参阅 last (), firstKey ()，和 isEmpty ().

[since 5.2] const T &QMultiMap:: first () const

这是重载函数。

该函数在 Qt 5.2 引入。

[since 5.2] const Key &QMultiMap:: firstKey () const

Returns a reference to the smallest key in the multi map. This function assumes that the multi map is not empty.

This executes in 常量时间 .

该函数在 Qt 5.2 引入。

另请参阅 lastKey (), first (), keyBegin ()，和 isEmpty ().

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

Inserts a new item with the key key 和值 value .

If there is already an item with the same key in the map, 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 ().

[since 5.1] QMultiMap::iterator QMultiMap:: insert ( QMultiMap::const_iterator pos , const Key & key , const T & value )

这是重载函数。

Inserts a new item with the key key and value value and with hint pos suggesting where to do the insert.

若 constBegin () is used as hint it indicates that the key is less than any key in the multi map while constEnd () suggests that the key is (strictly) larger than any key in the multi map. Otherwise the hint should meet the condition ( pos - 1). key () < key <= pos. key (). If the hint pos is wrong it is ignored and a regular insert is done.

If the hint is correct and the multi map is unshared, the insert executes in amortized 常量时间 .

If there is already an item with the same key in the map, this function will simply create a new one.

When creating a multi map from sorted data inserting the largest key first with constBegin () is faster than inserting in sorted order with constEnd (), since constEnd () - 1 (which is needed to check if the hint is valid) needs logarithmic time .

注意： Be careful with the hint. Providing an iterator from an older shared instance might crash but there is also a risk that it will silently corrupt both the multi map and the pos multi map.

该函数在 Qt 5.1 引入。

bool QMultiMap:: isEmpty () const

返回 true if the multi map contains no items; otherwise returns false.

另请参阅 size ().

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

这是重载函数。

返回第一个键具有值 value ，或 defaultKey if the multi map contains no item with value value . If no defaultKey is provided the function returns a default-constructed key .

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

另请参阅 value () 和 keys ().

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

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

该函数在 Qt 5.6 引入。

另请参阅 keyEnd () 和 firstKey ().

[since 5.6] QMultiMap::key_iterator QMultiMap:: keyEnd () const

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

该函数在 Qt 5.6 引入。

另请参阅 keyBegin () 和 lastKey ().

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

返回 STL 样式迭代器 pointing to the first entry in the multi map.

该函数在 Qt 5.10 引入。

另请参阅 keyValueEnd ().

[since 5.10] QMultiMap::const_key_value_iterator QMultiMap:: keyValueBegin () const

返回常量 STL 样式迭代器 pointing to the first entry in the multi map.

该函数在 Qt 5.10 引入。

另请参阅 keyValueEnd ().

[since 5.10] QMultiMap::key_value_iterator QMultiMap:: keyValueEnd ()

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

该函数在 Qt 5.10 引入。

另请参阅 keyValueBegin ().

[since 5.10] QMultiMap::const_key_value_iterator QMultiMap:: keyValueEnd () const

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

该函数在 Qt 5.10 引入。

另请参阅 keyValueBegin ().

QList < Key > QMultiMap:: keys () const

Returns a list containing all the keys in the multi map in ascending order. Keys that occur multiple times in the multi map 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 ().

QList < Key > QMultiMap:: keys (const T & value ) const

这是重载函数。

Returns a list containing all the keys associated with value value in ascending order.

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

[since 5.2] T &QMultiMap:: last ()

Returns a reference to the last value in the multi map, that is the value mapped to the largest key. This function assumes that the map is not empty.

When unshared (or const version is called), this executes in logarithmic time .

该函数在 Qt 5.2 引入。

另请参阅 first (), lastKey ()，和 isEmpty ().

[since 5.2] const T &QMultiMap:: last () const

这是重载函数。

该函数在 Qt 5.2 引入。

[since 5.2] const Key &QMultiMap:: lastKey () const

Returns a reference to the largest key in the multi map. This function assumes that the multi map is not empty.

This executes in logarithmic time .

该函数在 Qt 5.2 引入。

另请参阅 firstKey (), last (), keyEnd ()，和 isEmpty ().

QMultiMap::iterator QMultiMap:: lowerBound (const Key & key )

Returns an iterator pointing to the first item with key key in the map. If the map contains no item with key key , the function returns an iterator to the nearest item with a greater key.

范例： 

QMultiMap<int, QString> multimap;
multimap.insert(1, "one");
multimap.insert(5, "five");
multimap.insert(5, "five (2)");
multimap.insert(10, "ten");
multimap.lowerBound(0);      // returns iterator to (1, "one")
multimap.lowerBound(1);      // returns iterator to (1, "one")
multimap.lowerBound(2);      // returns iterator to (5, "five")
multimap.lowerBound(5);      // returns iterator to (5, "five")
multimap.lowerBound(6);      // returns iterator to (10, "ten")
multimap.lowerBound(10);     // returns iterator to (10, "ten")
multimap.lowerBound(999);    // returns end()

If the map contains multiple items with key key , this function returns an iterator that points to the most recently inserted value. The other values are accessible by incrementing the iterator. For example, here's some code that iterates over all the items with the same key: 

QMap<QString, int> multimap;
...
QMap<QString, int>::const_iterator i = multimap.lowerBound("HDR");
QMap<QString, int>::const_iterator upperBound = multimap.upperBound("HDR");
while (i != upperBound) {
    cout << i.value() << Qt::endl;
    ++i;
}

另请参阅 upperBound () 和 find ().

QMultiMap::const_iterator QMultiMap:: lowerBound (const Key & key ) const

这是重载函数。

QMultiMap::size_type QMultiMap:: remove (const Key & key )

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

另请参阅 clear () 和 take ().

QMultiMap::size_type QMultiMap:: remove (const Key & key , const T & value )

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

另请参阅 clear () 和 take ().

[since 6.1] template <typename Predicate> QMultiMap::size_type QMultiMap:: removeIf ( Predicate pred )

Removes all elements for which the predicate pred returns true from the multi map.

The function supports predicates which take either an argument of type QMultiMap<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 ().

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

Inserts a new item with the key key 和值 value .

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

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

另请参阅 insert ().

QMultiMap::size_type QMultiMap:: size () const

Returns the number of (key, value) pairs in the multi map.

另请参阅 isEmpty () 和 count ().

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

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

T QMultiMap:: take (const Key & key )

Removes the item with the key key from the multi map and returns the value associated with it.

If the item does not exist in the multi map, the function simply returns a 默认构造值 . If there are multiple items for key in the map, only the most recently inserted one is removed and returned.

若不使用返回值， remove () 效率更高。

另请参阅 remove ().

std::multimap < Key , T > QMultiMap:: toStdMultiMap () const &

Returns an STL multi map equivalent to this QMultiMap .

QList < Key > QMultiMap:: uniqueKeys () const

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

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

Inserts all the items in the other map into this map. If a key is common to both maps, the resulting map will contain the key multiple times.

QMultiMap < Key , T > &QMultiMap:: unite ( QMultiMap < Key , T > && other )

Moves all the items from the other map into this map. If a key is common to both maps, the resulting map will contain the key multiple times.

若 other is shared, then the items will be copied instead.

QMultiMap::iterator QMultiMap:: upperBound (const Key & key )

Returns an iterator pointing to the item that immediately follows the last item with key key in the map. If the map contains no item with key key , the function returns an iterator to the nearest item with a greater key.

范例： 

QMultiMap<int, QString> multimap;
multimap.insert(1, "one");
multimap.insert(5, "five");
multimap.insert(5, "five (2)");
multimap.insert(10, "ten");
multimap.upperBound(0);      // returns iterator to (1, "one")
multimap.upperBound(1);      // returns iterator to (5, "five")
multimap.upperBound(2);      // returns iterator to (5, "five")
multimap.lowerBound(5);      // returns iterator to (5, "five (2)")
multimap.lowerBound(6);      // returns iterator to (10, "ten")
multimap.upperBound(10);     // returns end()
multimap.upperBound(999);    // returns end()

另请参阅 lowerBound () 和 find ().

QMultiMap::const_iterator QMultiMap:: upperBound (const Key & key ) const

这是重载函数。

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

Returns the value associated with the key key .

If the multi map contains no item with key key ，函数返回 defaultValue . If no defaultValue is specified, the function returns a 默认构造值 . If there are multiple items for key in the multi map, the value of the most recently inserted one is returned.

另请参阅 key (), values ()，和 contains ().

QList < T > QMultiMap:: values () const

Returns a list containing all the values in the map, in ascending order of their keys. 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.

另请参阅 keys () 和 value ().

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

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

另请参阅 keys () 和 value ().

相关非成员

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

Removes all elements for which the predicate pred returns true from the multi map map .

The function supports predicates which take either an argument of type QMultiMap<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。

bool operator!= (const QMultiMap < Key , T > & lhs , const QMultiMap < Key , T > & rhs )

返回 true if lhs 不等于 rhs ；否则返回 false .

Two multi maps are considered equal if they contain the same (key, value) pairs, in the same order (which matters for duplicate keys).

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

另请参阅 operator== ().

template <typename Key, typename T> QDataStream & operator<< ( QDataStream & out , const QMultiMap < Key , T > & map )

Writes the multi map map 到流 out .

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

另请参阅 QDataStream 运算符格式 .

bool operator== (const QMultiMap < Key , T > & lhs , const QMultiMap < Key , T > & rhs )

返回 true if lhs 等于 rhs ；否则返回 false。

Two multi maps are considered equal if they contain the same (key, value) pairs, in the same order (which matters for duplicate keys).

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

另请参阅 operator!= ().

template <typename Key, typename T> QDataStream & operator>> ( QDataStream & in , QMultiMap < Key , T > & map )

读取映射从流 in into map .

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

另请参阅 QDataStream 运算符格式 .