QMap 類

template <typename Key, typename T> class QMap

QMap 類是提供關聯數組的模闆類。 更多...

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

• 所有成員列錶，包括繼承成員
• QMap is part of 隱式共享類 .

此類 相等可比較 .

注意： 此類的所有函數 可重入 .

公共類型

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

公共函數

	QMap ()
	QMap (const std::map<Key, T> & other )
	QMap (std::initializer_list<std::pair<Key, T>> list )
	QMap (std::map<Key, T> && other )
	QMap (const QMap<Key, T> & other )
	QMap (QMap<Key, T> && other )
	~QMap ()
(從 6.4 起) auto	asKeyValueRange () &&
(從 6.4 起) auto	asKeyValueRange () &
(從 6.4 起) auto	asKeyValueRange () const &&
(從 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 )
(從 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
void	insert (QMap<Key, T> && map )
void	insert (const QMap<Key, T> & map )
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 )
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 )
(從 6.1 起) 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 &
(從 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>	值 () const
QMap<Key, T> &	operator= (QMap<Key, T> && other )
QMap<Key, T> &	operator= (const QMap<Key, T> & other )
T &	operator[] (const Key & key )
T	operator[] (const Key & key ) const

相關非成員

(從 6.1 起) qsizetype	erase_if (QMap<Key, T> & map , Predicate pred )
(從 6.8 起) size_t	qHash (const QMap<Key, T> & key , size_t seed = 0)
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 )

詳細描述

QMap<Key, T> 是一種 Qt 一般 容器類 。它存儲 (key, value) 對，並提供按 Key 的快速查找。

QMap 和 QHash 提供非常類似的功能。差異是：

• QHash 提供比 QMap 平均更快的查找。(見 算法的復雜性 瞭解細節。)
• 當遍曆 QHash ，項是任意次序。采用 QMap，項始終按鍵排序。
• Key 類型對於 QHash 必須提供 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.

這裏是 QMap 範例具有 QString 鍵和 int 值：

QMap<QString, int> map;
					

要將 (key, value) 對插入映射，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 默認構造值 .

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;
}
					

要避免此問題，替換 map[i] with map.value(i) 在以上代碼中。

If you want to navigate through all the (key, value) pairs stored in a QMap, you can use an iterator. QMap provides both Java 風格迭代器 ( QMapIterator and QMutableMapIterator ) 和 STL 樣式迭代器 ( 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 可賦值數據類型 . This covers most data types you are likely to encounter, but the compiler won't let you, for example, store a QWidget 作為值；取而代之，存儲 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 為 true。

範例：

#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.

另請參閱 QMapIterator , QMutableMapIterator , QHash ，和 QSet .

成員類型文檔編製

QMap:: ConstIterator

Qt 樣式同義詞 QMap::const_iterator .

QMap:: Iterator

Qt 樣式同義詞 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.

另請參閱 QKeyValueIterator .

[alias] QMap:: difference_type

typedef 對於 ptrdiff_t。為兼容 STL 提供。

[alias] QMap:: key_type

typedef 對於 Key。為兼容 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.

另請參閱 QKeyValueIterator .

[alias] QMap:: mapped_type

typedef 對於 T。為兼容 STL 提供。

[alias] QMap:: size_type

typedef 對於 int。為兼容 STL 提供。

成員函數文檔編製

[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.

These functions were introduced in Qt 6.4.

另請參閱 QKeyValueIterator .

QMap:: QMap ()

Constructs an empty map.

另請參閱 clear ().

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

構造副本為 other .

另請參閱 toStdMap ().

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 ( std::map < Key , T > && other )

Constructs a map by moving from other .

另請參閱 toStdMap ().

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

構造副本為 other .

This operation occurs in 常量時間 , because QMap is 隱式共享 . 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 綫性時間 .

另請參閱 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 ()

返迴 STL 樣式迭代器 pointing to the first item in the map.

另請參閱 constBegin () 和 end ().

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

這是重載函數。

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

返迴常量 STL 樣式迭代器 pointing to the first item in the map.

另請參閱 begin () 和 cend ().

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

返迴常量 STL 樣式迭代器 pointing to the imaginary item after the last item in the map.

另請參閱 cbegin () 和 end ().

void QMap:: clear ()

Removes all items from the map.

另請參閱 remove ().

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

返迴常量 STL 樣式迭代器 pointing to the first item in the map.

另請參閱 begin () 和 constEnd ().

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

返迴常量 STL 樣式迭代器 pointing to the imaginary item after the last item in the map.

另請參閱 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 ，函數返迴 constEnd ().

另請參閱 find ().

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

返迴常量 STL 樣式迭代器 pointing to the first entry in the map.

另請參閱 keyValueBegin ().

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

返迴常量 STL 樣式迭代器 pointing to the imaginary entry after the last entry in the map.

另請參閱 constKeyValueBegin ().

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

返迴 true if the map contains an item with key key ；否則返迴 false .

另請參閱 count ().

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

Returns the number of items associated with key key .

另請參閱 contains ().

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

如同 size ().

這是重載函數。

bool QMap:: empty () const

此函數為兼容 STL (標準模闆庫) 提供。它相當於 isEmpty (), returning true if the map is empty; otherwise returning false.

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

返迴 STL 樣式迭代器 pointing to the imaginary item after the last item in the map.

另請參閱 begin () 和 constEnd ().

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

這是重載函數。

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

這是重載函數。

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.

另請參閱 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： 範圍 [first, last) must be a valid range in *this .

該函數在 Qt 6.0 引入。

另請參閱 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 ，函數返迴 end ().

另請參閱 constFind (), value (), 值 (), lowerBound ()，和 upperBound ().

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

這是重載函數。

T &QMap:: 第一 ()

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 常量時間 .

另請參閱 last (), firstKey ()，和 isEmpty ().

const T &QMap:: 第一 () const

這是重載函數。

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 常量時間 .

另請參閱 lastKey (), first (), keyBegin ()，和 isEmpty ().

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

Moves all the items from map 進此映射。

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.

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

插入所有項在 map 進此映射。

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

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 )

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 常量時間 .

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.

這是重載函數。

bool QMap:: isEmpty () const

返迴 true 若映射不包含項；否則返迴 false。

另請參閱 size ().

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

返迴第 1 個鍵具有值 value ，或 defaultKey if the map contains no item with value value . If no defaultKey is provided the function returns a default-constructed key .

此函數可能很慢 ( 綫性時間 )，因為 QMap 's internal data structure is optimized for fast lookup by key, not by value.

另請參閱 value () 和 keys ().

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

返迴常量 STL 樣式迭代器 pointing to the first key in the map.

另請參閱 keyEnd () 和 firstKey ().

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

返迴常量 STL 樣式迭代器 pointing to the imaginary item after the last key in the map.

另請參閱 keyBegin () 和 lastKey ().

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

返迴 STL 樣式迭代器 pointing to the first entry in the map.

另請參閱 keyValueEnd ().

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

返迴常量 STL 樣式迭代器 pointing to the first entry in the map.

另請參閱 keyValueEnd ().

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

返迴 STL 樣式迭代器 pointing to the imaginary entry after the last entry in the map.

另請參閱 keyValueBegin ().

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

返迴常量 STL 樣式迭代器 pointing to the imaginary entry after the last entry in the map.

另請參閱 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 值 ().

此函數創建新列錶，按 綫性時間 . The time and memory use that entails can be avoided by iterating from keyBegin () 到 keyEnd ().

另請參閱 值 () 和 key ().

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

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

此函數可能很慢 ( 綫性時間 )，因為 QMap 's internal data structure is optimized for fast lookup by key, not by value.

這是重載函數。

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 .

另請參閱 first (), lastKey ()，和 isEmpty ().

const T &QMap:: last () const

這是重載函數。

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 .

另請參閱 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.

另請參閱 upperBound () 和 find ().

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

這是重載函數。

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.

另請參閱 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.

該函數在 Qt 6.1 引入。

另請參閱 clear () 和 take ().

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

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

另請參閱 isEmpty () 和 count ().

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

Swaps this map with other 。此操作很快且從不失敗。

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 默認構造值 .

若不使用返迴值， remove () 效率更高。

另請參閱 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 () &&

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.

這是重載函數。

該函數在 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.

範例：

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()
					

另請參閱 lowerBound () 和 find ().

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

這是重載函數。

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 ，函數返迴 defaultValue . If no defaultValue is specified, the function returns a 默認構造值 .

另請參閱 key (), 值 (), contains ()，和 operator[] ().

QList < T > QMap:: 值 () const

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

此函數創建新列錶，按 綫性時間 . The time and memory use that entails can be avoided by iterating from keyValueBegin () 到 keyValueEnd ().

另請參閱 keys () 和 value ().

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

移動賦值 other 到此 QMap 實例。

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

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

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

Returns the value associated with the key key 作為可修改引用。

If the map contains no item with key key , the function inserts a 默認構造值 into the map with key key , and returns a reference to it.

另請參閱 insert () 和 value ().

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

如同 value ().

這是重載函數。

相關非成員

[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.

該函數在 Qt 6.1 引入。

[since 6.8] size_t qHash (const QMap < Key , T > & key , size_t seed = 0)

返迴哈希值為 key ，使用 seed 做計算種子。

類型 Key and T must be supported by qHash().

該函數在 Qt 6.8 引入。

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

返迴 true if lhs 不等於 rhs ；否則返迴 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==() .

另請參閱 operator== ().

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

寫入映射 map 到流 out .

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

另請參閱 QDataStream 運算符格式 .

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

返迴 true if lhs 等於 rhs ；否則返迴 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==() .

另請參閱 operator!= ().

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

讀取映射從流 in into map .

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

另請參閱 QDataStream 運算符格式 .

內容

1. 公共類型

2. 公共函數

3. 相關非成員

4. 詳細描述