QMap 类

template <typename Key, typename T> class QMap

QMap 类是提供关联数组的模板类。 更多...

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

• 所有成员列表，包括继承成员
• QMap is part of 隐式共享类 .

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

	QMap ()
	QMap (std::initializer_list<std::pair<Key, T>> list )
	QMap (const std::map<Key, T> & other )
	QMap (std::map<Key, T> && other )
	QMap (const QMap<Key, T> & other )
	QMap (QMap<Key, T> && other )
	~QMap ()
(从 6.4 起) auto	asKeyValueRange () &
(从 6.4 起) auto	asKeyValueRange () const &
(从 6.4 起) auto	asKeyValueRange () &&
(从 6.4 起) auto	asKeyValueRange () const &&
QMap<Key, T>::iterator	begin ()
QMap<Key, T>::const_iterator	begin () const
QMap<Key, T>::const_iterator	cbegin () const
QMap<Key, T>::const_iterator	cend () const
void	clear ()
QMap<Key, T>::const_iterator	constBegin () const
QMap<Key, T>::const_iterator	constEnd () const
QMap<Key, T>::const_iterator	constFind (const Key & key ) const
QMap<Key, T>::const_key_value_iterator	constKeyValueBegin () const
QMap<Key, T>::const_key_value_iterator	constKeyValueEnd () const
bool	contains (const Key & key ) const
QMap<Key, T>::size_type	count (const Key & key ) const
QMap<Key, T>::size_type	count () const
bool	empty () const
QMap<Key, T>::iterator	end ()
QMap<Key, T>::const_iterator	end () const
std::pair<QMap<Key, T>::iterator, QMap<Key, T>::iterator>	equal_range (const Key & key )
std::pair<QMap<Key, T>::const_iterator, QMap<Key, T>::const_iterator>	equal_range (const Key & key ) const
QMap<Key, T>::iterator	erase (QMap<Key, T>::const_iterator pos )
(从 6.0 起) QMap<Key, T>::iterator	erase (QMap<Key, T>::const_iterator first , QMap<Key, T>::const_iterator last )
QMap<Key, T>::iterator	find (const Key & key )
QMap<Key, T>::const_iterator	find (const Key & key ) const
T &	first ()
const T &	first () const
const Key &	firstKey () const
QMap<Key, T>::iterator	insert (const Key & key , const T & value )
QMap<Key, T>::iterator	insert (QMap<Key, T>::const_iterator pos , const Key & key , const T & value )
void	insert (const QMap<Key, T> & map )
void	insert (QMap<Key, T> && map )
bool	isEmpty () const
Key	key (const T & value , const Key & defaultKey = Key()) const
QMap<Key, T>::key_iterator	keyBegin () const
QMap<Key, T>::key_iterator	keyEnd () const
QMap<Key, T>::key_value_iterator	keyValueBegin ()
QMap<Key, T>::const_key_value_iterator	keyValueBegin () const
QMap<Key, T>::key_value_iterator	keyValueEnd ()
QMap<Key, T>::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
QMap<Key, T>::iterator	lowerBound (const Key & key )
QMap<Key, T>::const_iterator	lowerBound (const Key & key ) const
QMap<Key, T>::size_type	remove (const Key & key )
(since 6.1) QMap<Key, T>::size_type	removeIf (Predicate pred )
QMap<Key, T>::size_type	size () const
void	swap (QMap<Key, T> & other )
T	take (const Key & key )
std::map<Key, T>	toStdMap () const &
(从 6.0 起) std::map<Key, T>	toStdMap () &&
QMap<Key, T>::iterator	upperBound (const Key & key )
QMap<Key, T>::const_iterator	upperBound (const Key & key ) const
T	value (const Key & key , const T & defaultValue = T()) const
QList<T>	values () const
QMap<Key, T> &	operator= (const QMap<Key, T> & other )
QMap<Key, T> &	operator= (QMap<Key, T> && other )
T &	operator[] (const Key & key )
T	operator[] (const Key & key ) const

相关非成员

(since 6.1) qsizetype	erase_if (QMap<Key, T> & map , Predicate pred )
bool	operator!= (const QMap<Key, T> & lhs , const QMap<Key, T> & rhs )
QDataStream &	operator<< (QDataStream & out , const QMap<Key, T> & map )
bool	operator== (const QMap<Key, T> & lhs , const QMap<Key, T> & rhs )
QDataStream &	operator>> (QDataStream & in , QMap<Key, T> & map )

详细描述

QMap<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。

QMap 和 QHash 提供非常类似的功能。差异是：

• QHash 提供比 QMap 平均更快的查找。(见 算法的复杂性 了解细节。)
• 当遍历 QHash ，项是任意次序。采用 QMap，项始终按键排序。
• Key 类型对于 QHash 必须提供 operator==() 和全局 qHash (Key) function. The key type of a QMap 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 QMap 范例具有 QString 键和 int 值：

QMap<QString, int> map;
					

要将 (key, value) 对插入映射，可以使用 operator[]()：

map["one"] = 1;
map["three"] = 3;
map["seven"] = 7;
					

This inserts the following three (key, value) pairs into the QMap: ("one", 1), ("three", 3), and ("seven", 7). Another way to insert items into the map is to use insert ():

map.insert("twelve", 12);
					

要查找值，使用 operator[]() 或 value ():

int num1 = map["thirteen"];
int num2 = map.value("thirteen");
					

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 (map.contains("TIMEOUT"))
    timeout = map.value("TIMEOUT");
					

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 = map.value("TIMEOUT", 30);
					

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

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

要避免此问题，替换 map[i] with map.value(i) 在以上代码中。

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

QMapIterator<QString, int> i(map);
while (i.hasNext()) {
    i.next();
    cout << qPrintable(i.key()) << ": " << i.value() << endl;
}
					

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

for (auto i = map.cbegin(), end = map.cend(); i != end; ++i)
    cout << qPrintable(i.key()) << ": " << i.value() << endl;
					

The items are traversed in ascending key order.

A QMap allows only one value per key. If you call insert () with a key that already exists in the QMap, the previous value will be erased. For example:

map.insert("plenty", 100);
map.insert("plenty", 2000);
// map.value("plenty") == 2000
					

However, you can store multiple values per key by using QMultiMap .

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

QMap<QString, int> map;
...
for (int value : std::as_const(map))
    cout << value << endl;
					

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

QMap'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, QMap's key type must provide operator<(). QMap uses it to keep its items sorted, and assumes that two keys x and y are equivalent 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 QMapIterator , QMutableMapIterator , QHash ，和 QSet .

成员类型文档编制

QMap:: ConstIterator

Qt 样式同义词 QMap::const_iterator .

QMap:: Iterator

Qt 样式同义词 QMap::iterator .

QMap:: const_key_value_iterator

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

QMap::const_key_value_iterator is essentially the same as QMap::const_iterator with the difference that operator*() returns a key/value pair instead of a value.

另请参阅 QKeyValueIterator .

[alias] QMap:: difference_type

typedef 对于 ptrdiff_t。为兼容 STL 提供。

[alias] QMap:: key_type

typedef 对于 Key。为兼容 STL 提供。

QMap:: key_value_iterator

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

QMap::key_value_iterator is essentially the same as QMap::iterator with the difference that operator*() returns a key/value pair instead of a value.

另请参阅 QKeyValueIterator .

[alias] QMap:: mapped_type

typedef 对于 T。为兼容 STL 提供。

[alias] QMap:: size_type

typedef 对于 int。为兼容 STL 提供。

成员函数文档编制

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

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

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

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

Returns a range object that allows iteration over this map 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:

QMap<QString, int> map;
map.insert("January", 1);
map.insert("February", 2);
// ...
map.insert("December", 12);
for (auto [key, value] : map.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 map. Specifically, mutating the value will modify the map itself.

该函数在 Qt 6.4 引入。

另请参阅 QKeyValueIterator .

QMap:: QMap ()

Constructs an empty map.

另请参阅 clear ().

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

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

[explicit] QMap:: QMap (const std::map < Key , T > & other )

构造副本为 other .

另请参阅 toStdMap ().

[explicit] QMap:: QMap ( std::map < Key , T > && other )

Constructs a map by moving from other .

另请参阅 toStdMap ().

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

构造副本为 other .

This operation occurs in 常量时间 , because QMap is 隐式共享 . This makes returning a QMap 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] QMap:: QMap ( QMap < Key , T > && other )

Move-constructs a QMap instance.

[default] QMap:: ~QMap ()

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

QMap < Key , T > ::iterator QMap:: begin ()

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

另请参阅 constBegin () 和 end ().

QMap < Key , T > ::const_iterator QMap:: begin () const

这是重载函数。

QMap < Key , T > ::const_iterator QMap:: cbegin () const

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

另请参阅 begin () 和 cend ().

QMap < Key , T > ::const_iterator QMap:: cend () const

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

另请参阅 cbegin () 和 end ().

void QMap:: clear ()

Removes all items from the map.

另请参阅 remove ().

QMap < Key , T > ::const_iterator QMap:: constBegin () const

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

另请参阅 begin () 和 constEnd ().

QMap < Key , T > ::const_iterator QMap:: constEnd () const

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

另请参阅 constBegin () 和 end ().

QMap < Key , T > ::const_iterator QMap:: constFind (const Key & key ) const

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

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

另请参阅 find ().

QMap < Key , T > ::const_key_value_iterator QMap:: constKeyValueBegin () const

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

另请参阅 keyValueBegin ().

QMap < Key , T > ::const_key_value_iterator QMap:: constKeyValueEnd () const

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

另请参阅 constKeyValueBegin ().

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

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

另请参阅 count ().

QMap < Key , T > ::size_type QMap:: count (const Key & key ) const

Returns the number of items associated with key key .

另请参阅 contains ().

QMap < Key , T > ::size_type QMap:: count () const

这是重载函数。

如同 size ().

bool QMap:: 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.

QMap < Key , T > ::iterator QMap:: end ()

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

另请参阅 begin () 和 constEnd ().

QMap < Key , T > ::const_iterator QMap:: end () const

这是重载函数。

std::pair < QMap < Key , T > ::iterator , QMap < Key , T > ::iterator > QMap:: equal_range (const Key & key )

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

std::pair < QMap < Key , T > ::const_iterator , QMap < Key , T > ::const_iterator > QMap:: equal_range (const Key & key ) const

这是重载函数。

QMap < Key , T > ::iterator QMap:: erase ( QMap < Key , T > ::const_iterator pos )

Removes the (key, value) pair pointed to by the iterator pos from the 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] QMap < Key , T > ::iterator QMap:: erase ( QMap < Key , T > ::const_iterator first , QMap < Key , T > ::const_iterator last )

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

QMap < Key , T > ::iterator QMap:: find (const Key & key )

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

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

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

QMap < Key , T > ::const_iterator QMap:: find (const Key & key ) const

这是重载函数。

T &QMap:: first ()

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

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

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

const T &QMap:: first () const

这是重载函数。

const Key &QMap:: firstKey () const

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

This executes in 常量时间 .

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

QMap < Key , T > ::iterator QMap:: 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 key key , that item's value is replaced with value .

Returns an iterator pointing to the new/updated element.

QMap < Key , T > ::iterator QMap:: insert ( QMap < Key , T > ::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 map while constEnd () suggests that the key is (strictly) larger than any key in the 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 there is already an item with the key key , that item's value is replaced with value .

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

When creating a 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 map and the pos map.

Returns an iterator pointing to the new/updated element.

void QMap:: insert (const QMap < Key , T > & map )

插入所有项在 map 进此映射。

If a key is common to both maps, its value will be replaced with the value stored in map .

void QMap:: insert ( QMap < Key , T > && map )

Moves all the items from map 进此映射。

If a key is common to both maps, its value will be replaced with the value stored in map .

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

bool QMap:: isEmpty () const

返回 true 若映射不包含项；否则返回 false。

另请参阅 size ().

Key QMap:: 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 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 QMap 's internal data structure is optimized for fast lookup by key, not by value.

另请参阅 value () 和 keys ().

QMap < Key , T > ::key_iterator QMap:: keyBegin () const

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

另请参阅 keyEnd () 和 firstKey ().

QMap < Key , T > ::key_iterator QMap:: keyEnd () const

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

另请参阅 keyBegin () 和 lastKey ().

QMap < Key , T > ::key_value_iterator QMap:: keyValueBegin ()

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

另请参阅 keyValueEnd ().

QMap < Key , T > ::const_key_value_iterator QMap:: keyValueBegin () const

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

另请参阅 keyValueEnd ().

QMap < Key , T > ::key_value_iterator QMap:: keyValueEnd ()

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

另请参阅 keyValueBegin ().

QMap < Key , T > ::const_key_value_iterator QMap:: keyValueEnd () const

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

另请参阅 keyValueBegin ().

QList < Key > QMap:: keys () const

Returns a list containing all the keys in the map in ascending order.

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 > QMap:: 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 QMap 's internal data structure is optimized for fast lookup by key, not by value.

T &QMap:: last ()

Returns a reference to the last value in the 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 .

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

const T &QMap:: last () const

这是重载函数。

const Key &QMap:: lastKey () const

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

This executes in logarithmic time .

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

QMap < Key , T > ::iterator QMap:: 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.

另请参阅 upperBound () 和 find ().

QMap < Key , T > ::const_iterator QMap:: lowerBound (const Key & key ) const

这是重载函数。

QMap < Key , T > ::size_type QMap:: remove (const Key & key )

Removes all the items that have the key key from the map. Returns the number of items removed which will be 1 if the key exists in the map, and 0 otherwise.

另请参阅 clear () 和 take ().

[since 6.1] template <typename Predicate> QMap < Key , T > ::size_type QMap:: removeIf ( Predicate pred )

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

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

QMap < Key , T > ::size_type QMap:: size () const

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

另请参阅 isEmpty () 和 count ().

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

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

T QMap:: take (const Key & key )

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

If the item does not exist in the map, the function simply returns a 默认构造值 .

若不使用返回值， remove () 效率更高。

另请参阅 remove ().

std::map < Key , T > QMap:: toStdMap () const &

Returns an STL map equivalent to this QMap .

[since 6.0] std::map < Key , T > QMap:: toStdMap () &&

这是重载函数。

注意： Calling this function will leave this QMap in the partially-formed state, in which the only valid operations are destruction or assignment of a new value.

该函数在 Qt 6.0 引入。

QMap < Key , T > ::iterator QMap:: 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：

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

另请参阅 lowerBound () 和 find ().

QMap < Key , T > ::const_iterator QMap:: upperBound (const Key & key ) const

这是重载函数。

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

Returns the value associated with the key key .

If the 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 .

另请参阅 key (), values (), contains ()，和 operator[] ().

QList < T > QMap:: values () const

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

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

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

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

移动赋值 other 到此 QMap 实例。

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

Returns the value associated with the key key 作为可修改引用。

If the map contains no item with key key , the function inserts a 默认构造值 into the map with key key , and returns a reference to it.

另请参阅 insert () 和 value ().

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

这是重载函数。

如同 value ().

相关非成员

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

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

The function supports predicates which take either an argument of type QMap<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 QMap < Key , T > & lhs , const QMap < Key , T > & rhs )

返回 true if lhs 不等于 rhs ；否则返回 false。

Two maps are considered equal if they contain the same (key, value) pairs.

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 QMap < Key , T > & map )

写入映射 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 QMap < Key , T > & lhs , const QMap < Key , T > & rhs )

返回 true if lhs 等于 rhs ；否则返回 false。

Two maps are considered equal if they contain the same (key, value) pairs.

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 , QMap < 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 .

内容

• 公共类型

• 公共函数

• 相关非成员

• 详细描述