QHash 类是提供基于哈希表的字典的模板类。 更多...
| 头： | #include <QHash> |
| 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 .
| 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 |
| QHash (InputIterator begin , InputIterator end ) | |
| QHash (QHash<Key, T> && other ) | |
| QHash (const QHash<Key, T> & other ) | |
| QHash (std::initializer_list<std::pair<Key, T> > list ) | |
| QHash () | |
| QHash<Key, T> & | operator= (QHash<Key, T> && other ) |
| QHash<Key, T> & | operator= (const QHash<Key, T> & other ) |
| ~QHash () | |
| QHash::iterator | begin () |
| QHash::const_iterator | begin () const |
| qsizetype | capacity () const |
| QHash::const_iterator | cbegin () const |
| QHash::const_iterator | cend () const |
| void | clear () |
| QHash::const_iterator | constBegin () const |
| QHash::const_iterator | constEnd () const |
| QHash::const_iterator | constFind (const Key & key ) const |
| QHash::const_key_value_iterator | constKeyValueBegin () const |
| QHash::const_key_value_iterator | constKeyValueEnd () const |
| bool | contains (const Key & key ) const |
| qsizetype | count (const Key & key ) const |
| qsizetype | count () const |
| QHash::iterator | emplace (const Key & key , Args &&... args ) |
| QHash::iterator | emplace (Key && key , Args &&... args ) |
| bool | empty () const |
| QHash::iterator | end () |
| QHash::const_iterator | end () const |
| QHash::iterator | erase (QHash::const_iterator pos ) |
| QHash::iterator | find (const Key & key ) |
| QHash::const_iterator | find (const Key & key ) const |
| QHash::iterator | insert (const Key & key , const T & value ) |
| void | insert (const QHash<Key, T> & other ) |
| bool | isEmpty () const |
| Key | key (const T & value , const Key & defaultKey = Key()) const |
| QHash::key_iterator | keyBegin () const |
| QHash::key_iterator | keyEnd () const |
| QHash::key_value_iterator | keyValueBegin () |
| QHash::const_key_value_iterator | keyValueBegin () const |
| QHash::key_value_iterator | keyValueEnd () |
| QHash::const_key_value_iterator | keyValueEnd () const |
| QList<Key> | keys () const |
| QList<Key> | keys (const T & value ) const |
| float | load_factor () const |
| bool | remove (const Key & key ) |
| qsizetype | removeIf (Predicate pred ) |
| void | reserve (qsizetype size ) |
| qsizetype | size () const |
| void | squeeze () |
| void | swap (QHash<Key, T> & other ) |
| T | take (const Key & key ) |
| T | value (const Key & key , const T & defaultValue = T()) const |
| QList<T> | values () const |
| bool | operator!= (const QHash<Key, T> & other ) const |
| bool | operator== (const QHash<Key, T> & other ) const |
| T & | operator[] (const Key & key ) |
| const T | operator[] (const Key & key ) const |
| qsizetype | erase_if (QHash<Key, T> & hash , Predicate pred ) |
| size_t | qHash (const QGeoCoordinate & coordinate , size_t seed ) |
| size_t | qHash (const QOcspResponse & response , size_t seed ) |
| size_t | qHash (const QMqttTopicFilter & filter , size_t seed ) |
| size_t | qHash (const QStringRef & key , size_t seed ) |
| size_t | qHash (const QUrl & url , size_t seed = 0) |
| size_t | qHash (const QSslCertificate & key , size_t seed ) |
| size_t | qHash (const QMqttTopicName & name , size_t seed ) |
| size_t | qHash (const QDateTime & key , size_t seed = 0) |
| size_t | qHash (QSslEllipticCurve curve , size_t seed ) |
| size_t | qHash (QDate key , size_t seed = 0) |
| size_t | qHash (const QSslError & key , size_t seed ) |
| size_t | qHash (QTime key , size_t seed = 0) |
| size_t | qHash (const std::pair<T1, T2> & key , size_t seed = 0) |
| size_t | qHash (char key , size_t seed = 0) |
| size_t | qHash (uchar key , size_t seed = 0) |
| size_t | qHash (signed char key , size_t seed = 0) |
| size_t | qHash (ushort key , size_t seed = 0) |
| size_t | qHash (short key , size_t seed = 0) |
| size_t | qHash (uint key , size_t seed = 0) |
| size_t | qHash (int key , size_t seed = 0) |
| size_t | qHash (ulong key , size_t seed = 0) |
| size_t | qHash (long key , size_t seed = 0) |
| size_t | qHash (quint64 key , size_t seed = 0) |
| size_t | qHash (qint64 key , size_t seed = 0) |
| size_t | qHash (char8_t key , size_t seed = 0) |
| size_t | qHash (char16_t key , size_t seed = 0) |
| size_t | qHash (char32_t key , size_t seed = 0) |
| size_t | qHash (wchar_t key , size_t seed = 0) |
| size_t | qHash (float key , size_t seed = 0) |
| size_t | qHash (double key , size_t seed = 0) |
| size_t | qHash (long double key , size_t seed = 0) |
| size_t | qHash (const QChar key , size_t seed = 0) |
| size_t | qHash (const QByteArray & key , size_t seed = 0) |
| size_t | qHash (const QByteArrayView & key , size_t seed = 0) |
| size_t | qHash (const QBitArray & key , size_t seed = 0) |
| size_t | qHash (const QString & key , size_t seed = 0) |
| size_t | qHash (QLatin1String key , size_t seed = 0) |
| size_t | qHash (const T * key , size_t seed = 0) |
| size_t | qHash (std::nullptr_t key , size_t seed = 0) |
| size_t | qHash (const QHash<Key, T> & key , size_t seed = 0) |
| size_t | qHash (QPoint key , size_t seed = 0) |
| size_t | qHash (const QSet<T> & key , size_t seed = 0) |
| size_t | qHash (const QVersionNumber & key , size_t seed = 0) |
| size_t | qHash (const QTypeRevision & key , size_t seed = 0) |
| size_t | qHashBits (const void * p , size_t len , size_t seed = 0) |
| size_t | qHashMulti (size_t seed , const T &... args ) |
| size_t | qHashMultiCommutative (size_t seed , const T &... args ) |
| size_t | qHashRange (InputIterator first , InputIterator last , size_t seed = 0) |
| size_t | qHashRangeCommutative (InputIterator first , InputIterator last , size_t seed = 0) |
| QDataStream & | operator<< (QDataStream & out , const QHash<Key, T> & hash ) |
| QDataStream & | operator>> (QDataStream & in , QHash<Key, T> & hash ) |
QHash<Key, T> 是一种 Qt 一般 容器类 。它存储 (键，值) 对，并提供键关联值的非常快速查找。
QHash 提供的功能非常类似于 QMap 。差异：
这里是 QHash 范例具有
QString
键和
int
值：
QHash<QString, int> hash;
要将 (键，值) 对插入哈希，可以使用 operator[]()：
hash["one"] = 1; hash["three"] = 3; hash["seven"] = 7;
This inserts the following three (key, value) pairs into the QHash: ("one", 1), ("three", 3), and ("seven", 7). Another way to insert items into the hash is to use insert ():
hash.insert("twelve", 12);
要查找值，使用 operator[]() 或 value ():
int num1 = hash["thirteen"]; int num2 = hash.value("thirteen");
If there is no item with the specified key in the hash, these functions return a 默认构造值 .
If you want to check whether the hash contains a particular key, use contains ():
int timeout = 30; if (hash.contains("TIMEOUT")) timeout = hash.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 = hash.value("TIMEOUT", 30);
In general, we recommend that you use contains () 和 value () rather than operator[]() for looking up a key in a hash. The reason is that operator[]() silently inserts an item into the hash if no item exists with the same key (unless the hash is const). For example, the following code snippet will create 1000 items in memory:
// WRONG QHash<int, QWidget *> hash; ... for (int i = 0; i < 1000; ++i) { if (hash[i] == okButton) cout << "Found button at index " << i << Qt::endl; }
要避免此问题，替换
hash[i]
with
hash.value(i)
在以上代码中。
Internally, QHash uses a hash table to perform lookups. This hash table automatically grows to provide fast lookups without wasting too much memory. You can still control the size of the hash table by calling reserve () if you already know approximately how many items the QHash will contain, but this isn't necessary to obtain good performance. You can also call capacity () to retrieve the hash table's size.
QHash will not shrink automatically if items are removed from the table. To minimize the memory used by the hash, call squeeze ().
If you want to navigate through all the (key, value) pairs stored in a QHash, you can use an iterator. QHash provides both Java 风格迭代器 ( QHashIterator and QMutableHashIterator ) 和 STL 样式迭代器 ( QHash::const_iterator and QHash::iterator ). Here's how to iterate over a QHash< QString , int> using a Java-style iterator:
QHashIterator<QString, int> i(hash); while (i.hasNext()) { i.next(); cout << i.key() << ": " << i.value() << Qt::endl; }
Here's the same code, but using an STL-style iterator:
QHash<QString, int>::const_iterator i = hash.constBegin(); while (i != hash.constEnd()) { cout << i.key() << ": " << i.value() << Qt::endl; ++i; }
QHash is unordered, so an iterator's sequence cannot be assumed to be predictable. If ordering by key is required, use a QMap .
A QHash allows only one value per key. If you call insert () with a key that already exists in the QHash, the previous value is erased. For example:
hash.insert("plenty", 100); hash.insert("plenty", 2000); // hash.value("plenty") == 2000
If you need to store multiple entries for the same key in the hash table, use QMultiHash .
If you only need to extract the values from a hash (not the keys), you can also use foreach :
QHash<QString, int> hash; ... foreach (int value, hash) cout << value << Qt::endl;
Items can be removed from the hash in several ways. One way is to call remove (); this will remove any item with the given key. Another way is to use QMutableHashIterator::remove (). In addition, you can clear the entire hash using clear ().
QHash 的键和值的数据类型必须是 可赋值数据类型 。例如，无法存储 QWidget 作为值；取而代之，存储 QWidget *.
A QHash's key type has additional requirements other than being an assignable data type: it must provide operator==(), and there must also be a hashing function that returns a hash value for an argument of the key's type.
The hashing function computes a numeric value based on a key. It can use any algorithm imaginable, as long as it always returns the same value if given the same argument. In other words, if
e1 == e2
，那么
hash(e1) == hash(e2)
must hold as well. However, to obtain good performance, the hashing function should attempt to return different hash values for different keys to the largest extent possible.
A hashing function for a key type
K
may be provided in two different ways.
The first way is by having an overload of
qHash()
in
K
's namespace. The
qHash()
function must have one of these signatures:
size_t qHash(K key); size_t qHash(const K &key); size_t qHash(K key, size_t seed); size_t qHash(const K &key, size_t seed);
The two-arguments overloads take an unsigned integer that should be used to seed the calculation of the hash function. This seed is provided by QHash in order to prevent a family of algorithmic complexity attacks . If both a one-argument and a two-arguments overload are defined for a key type, the latter is used by QHash (note that you can simply define a two-arguments version, and use a default value for the seed parameter).
The second way to provide a hashing function is by specializing the
std::hash
class for the key type
K
, and providing a suitable function call operator for it:
namespace std { template <> struct hash<K> { // seed is optional size_t operator()(const K &key, size_t seed = 0) const; }; }
The seed argument has the same meaning as for
qHash()
, and may be left out.
This second way allows to reuse the same hash function between QHash and the C++ Standard Library unordered associative containers. If both a
qHash()
overload and a
std::hash
specializations are provided for a type, then the
qHash()
overload is preferred.
Here's a partial list of the C++ and Qt types that can serve as keys in a QHash: any integer type (char, unsigned long, etc.), any pointer type,
QChar
,
QString
，和
QByteArray
. For all of these, the
<QHash>
header defines a
qHash
() function that computes an adequate hash value. Many other Qt classes also declare a
qHash
overload for their type; please refer to the documentation of each class.
If you want to use other types as the key, make sure that you provide operator==() and a hash implementation.
The convenience qHashMulti () function can be used to implement qHash () for a custom type, where one usually wants to produce a hash value from multiple fields:
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) { return e1.name() == e2.name() && e1.dateOfBirth() == e2.dateOfBirth(); } inline size_t qHash(const Employee &key, size_t seed) { return qHashMulti(seed, key.name(), key.dateOfBirth()); } #endif // EMPLOYEE_H
In the example above, we've relied on Qt's own implementation of qHash () 对于 QString and QDate to give us a hash value for the employee's name and date of birth respectively.
Note that the implementation of the qHash () overloads offered by Qt may change at any time. You 不必 rely on the fact that qHash () will give the same results (for the same inputs) across different Qt versions.
All hash tables are vulnerable to a particular class of denial of service attacks, in which the attacker carefully pre-computes a set of different keys that are going to be hashed in the same bucket of a hash table (or even have the very same hash value). The attack aims at getting the worst-case algorithmic behavior (O(n) instead of amortized O(1), see 算法的复杂性 for the details) when the data is fed into the table.
In order to avoid this worst-case behavior, the calculation of the hash value done by qHash () can be salted by a random seed, that nullifies the attack's extent. This seed is automatically generated by QHash once per process, and then passed by QHash as the second argument of the two-arguments overload of the qHash () 函数。
This randomization of QHash is enabled by default. Even though programs should never depend on a particular QHash ordering, there may be situations where you temporarily need deterministic behavior, for example for debugging or regression testing. To disable the randomization, define the environment variable
QT_HASH_SEED
to have the value 0. Alternatively, you can call the
QHashSeed::setDeterministicGlobalSeed
() 函数。
另请参阅 QHashIterator , QMutableHashIterator , QMap ，和 QSet .
Qt 样式同义词 QHash::const_iterator .
Qt 样式同义词 QHash::iterator .
[since 5.10]
QHash::
const_key_value_iterator
The QHash::const_key_value_iterator typedef provides an STL-style const iterator for QHash .
QHash::const_key_value_iterator is essentially the same as QHash::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]
QHash::
difference_type
typedef 对于 ptrdiff_t。为兼容 STL 提供。
[alias]
QHash::
key_type
typedef 对于 Key。为兼容 STL 提供。
[since 5.10]
QHash::
key_value_iterator
The QHash::key_value_iterator typedef provides an STL-style iterator for QHash .
QHash::key_value_iterator is essentially the same as QHash::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]
QHash::
mapped_type
typedef 对于 T。为兼容 STL 提供。
[alias]
QHash::
size_type
typedef 对于 int。为兼容 STL 提供。
Inserts a new element into the container. This new element is constructed in-place using args as the arguments for its construction.
Returns an iterator pointing to the new element.
[since 5.14]
template <typename InputIterator> QHash::
QHash
(
InputIterator
begin
,
InputIterator
end
)
Constructs a 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 5.2]
QHash::
QHash
(
QHash
<
Key
,
T
> &&
other
)
Move-constructs a QHash instance, making it point at the same object that other 所指向的。
该函数在 Qt 5.2 引入。
构造副本为 other .
This operation occurs in 常量时间 , because QHash is 隐式共享 . This makes returning a QHash 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= ().
[since 5.1]
QHash::
QHash
(
std::initializer_list
<
std::pair
<
Key
,
T
> >
list
)
Constructs a hash with a copy of each of the elements in the initializer list list .
该函数在 Qt 5.1 引入。
构造空哈希。
另请参阅 clear ().
[since 5.2]
QHash
<
Key
,
T
> &QHash::
operator=
(
QHash
<
Key
,
T
> &&
other
)
移动赋值 other 到此 QHash 实例。
该函数在 Qt 5.2 引入。
赋值 other to this hash and returns a reference to this hash.
Destroys the hash. References to the values in the hash and all iterators of this hash become invalid.
返回 STL 样式迭代器 指向哈希中的首项。
另请参阅 constBegin () 和 end ().
这是重载函数。
Returns the number of buckets in the QHash 的内部哈希表。
The sole purpose of this function is to provide a means of fine tuning QHash 's memory usage. In general, you will rarely ever need to call this function. If you want to know how many items are in the hash, call size ().
[since 5.0]
QHash::const_iterator
QHash::
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。
[since 5.0]
QHash::const_iterator
QHash::
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。
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 ().
返回常量 STL 样式迭代器 指向哈希中的首项。
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 ().
返回迭代器指向的项具有 key 在哈希中。
若哈希包含的项不具有 key ，函数返回 constEnd ().
另请参阅 find ().
[since 5.10]
QHash::const_key_value_iterator
QHash::
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]
QHash::const_key_value_iterator
QHash::
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 ().
返回
true
若哈希包含的项具有
key
；否则返回
false
.
另请参阅 count () 和 QMultiHash::contains ().
返回项数关联 key .
另请参阅 contains ().
这是重载函数。
如同 size ().
此函数为兼容 STL (标准模板库) 提供。它相当于
isEmpty
(), returning true if the hash is empty; otherwise returns
false
.
返回 STL 样式迭代器 pointing to the imaginary item after the last item in the hash.
这是重载函数。
[since 5.7]
QHash::iterator
QHash::
erase
(
QHash::const_iterator
pos
)
Removes the (key, value) pair associated with the iterator pos from the hash, and returns an iterator to the next item in the hash.
此函数从不会导致 QHash to rehash its internal data structure. This means that it can safely be called while iterating, and won't affect the order of items in the hash. For example:
QHash<QObject *, int> objectHash; ... QHash<QObject *, int>::iterator i = objectHash.find(obj); while (i != objectHash.end() && i.key() == obj) { if (i.value() == 0) { i = objectHash.erase(i); } else { ++i; } }
该函数在 Qt 5.7 引入。
另请参阅 remove (), take ()，和 find ().
返回迭代器指向的项具有 key 在哈希中。
若哈希包含的项不具有 key ，函数返回 end ().
If the hash contains multiple items with the 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:
QHash<QString, int> hash; ... QHash<QString, int>::const_iterator i = hash.find("HDR"); while (i != hash.end() && i.key() == "HDR") { cout << i.value() << Qt::endl; ++i; }
这是重载函数。
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 .
[since 5.15]
void
QHash::
insert
(const
QHash
<
Key
,
T
> &
other
)
Inserts all the items in the other hash into this hash.
If a key is common to both hashes, its value will be replaced with the value stored in other .
注意： 若 other contains multiple entries with the same key then the final value of the key is undefined.
该函数在 Qt 5.15 引入。
返回
true
if the hash contains no items; otherwise returns false.
另请参阅 size ().
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 QHash 's internal data structure is optimized for fast lookup by key, not by value.
[since 5.6]
QHash::key_iterator
QHash::
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]
QHash::key_iterator
QHash::
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]
QHash::key_value_iterator
QHash::
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]
QHash::const_key_value_iterator
QHash::
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]
QHash::key_value_iterator
QHash::
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]
QHash::const_key_value_iterator
QHash::
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 ().
Returns a list containing all the keys in the hash, in an arbitrary 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 ().
这是重载函数。
Returns a list containing all the keys associated with value value ，按任意次序。
此函数可能很慢 ( 线性时间 )，因为 QHash 's internal data structure is optimized for fast lookup by key, not by value.
Returns the current load factor of the QHash 's internal hash table. This is the same as capacity ()/ size (). The implementation used will aim to keep the load factor between 0.25 and 0.5. This avoids having too many hash table collisions that would degrade performance.
Even with a low load factor, the implementation of the hash table has a very low memory overhead.
This method purely exists for diagnostic purposes and you should rarely need to call it yourself.
Removes the item that has the key from the hash. Returns true if the key exists in the hash and the item has been removed, and false otherwise.
[since 6.1]
template <typename Predicate>
qsizetype
QHash::
removeIf
(
Predicate
pred
)
Removes all elements for which the predicate pred returns true from the hash.
The function supports predicates which take either an argument of type
QHash<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。
确保 QHash 's internal hash table has space to store at least size items without having to grow the hash table.
This implies that the hash table will contain at least 2 * size buckets to ensure good performance
This function is useful for code that needs to build a huge hash and wants to avoid repeated reallocation. For example:
QHash<QString, int> hash; hash.reserve(20000); for (int i = 0; i < 20000; ++i) hash.insert(keys[i], values[i]);
Ideally, size should be the maximum number of items expected in the hash. QHash will then choose the smallest possible number of buckets that will allow storing size items in the table without having to grow the internal hash table. If size is an underestimate, the worst that will happen is that the QHash will be a bit slower.
In general, you will rarely ever need to call this function. QHash 's internal hash table automatically grows to provide good performance without wasting too much memory.
另请参阅 squeeze () 和 capacity ().
返回哈希中的项数。
Reduces the size of the QHash 's internal hash table to save memory.
The sole purpose of this function is to provide a means of fine tuning QHash 's memory usage. In general, you will rarely ever need to call this function.
另请参阅 reserve () 和 capacity ().
交换哈希 other with this hash. This operation is very fast and never fails.
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 .
若不使用返回值， remove () 效率更高。
另请参阅 remove ().
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.
Returns a list containing all the values in the hash, in an arbitrary order.
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 ().
返回
true
if
other
不等于此哈希；否则返回
false
.
Two hashes are considered equal if they contain the same (key, value) pairs.
This function requires the value type to implement
operator==()
.
另请参阅 operator== ().
返回
true
if
other
is equal to this hash; otherwise returns false.
Two hashes are considered equal if they contain the same (key, value) pairs.
This function requires the value type to implement
operator==()
.
另请参阅 operator!= ().
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.
这是重载函数。
如同 value ().
[since 6.1]
template <typename Key, typename T, typename Predicate>
qsizetype
erase_if
(
QHash
<
Key
,
T
> &
hash
,
Predicate
pred
)
Removes all elements for which the predicate pred returns true from the hash hash .
The function supports predicates which take either an argument of type
QHash<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 5.0]
size_t
qHash
(const
QUrl
&
url
,
size_t
seed
= 0)
返回哈希值为 url 。若指定， seed 用于初始化哈希。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(const
QDateTime
&
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
QDate
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
QTime
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.7]
template <typename T1, typename T2>
size_t
qHash
(const
std::pair
<
T1
,
T2
> &
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
类型
T1
and
T2
must be supported by qHash().
该函数在 Qt 5.7 引入。
[since 5.0]
size_t
qHash
(
char
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
uchar
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
signed
char
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
ushort
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
short
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
uint
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
int
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
ulong
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
long
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
quint64
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
qint64
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 6.0]
size_t
qHash
(
char8_t
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 6.0]
size_t
qHash
(
char16_t
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 6.0]
size_t
qHash
(
char32_t
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 6.0]
size_t
qHash
(
wchar_t
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 5.3]
size_t
qHash
(
float
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.3 引入。
[since 5.3]
size_t
qHash
(
double
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.3 引入。
[since 5.3]
size_t
qHash
(
long
double
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.3 引入。
[since 5.0]
size_t
qHash
(const
QChar
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(const
QByteArray
&
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 6.0]
size_t
qHash
(const
QByteArrayView
&
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 5.0]
size_t
qHash
(const
QBitArray
&
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(const
QString
&
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
size_t
qHash
(
QLatin1String
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 5.0]
template <typename T>
size_t
qHash
(const
T
*
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.0 引入。
[since 6.0]
size_t
qHash
(
std::nullptr_t
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 5.8]
template <typename Key, typename T>
size_t
qHash
(const
QHash
<
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。
[since 6.0]
size_t
qHash
(
QPoint
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 5.5]
template <typename T>
size_t
qHash
(const
QSet
<
T
> &
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
The hash value is independent of the order of elements in key , that is, sets that contain the same elements hash to the same value.
该函数在 Qt 5.5 引入。
[since 5.6]
size_t
qHash
(const
QVersionNumber
&
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 5.6 引入。
[since 6.0]
size_t
qHash
(const
QTypeRevision
&
key
,
size_t
seed
= 0)
返回哈希值为 key ，使用 seed 做计算种子。
该函数在 Qt 6.0 引入。
[since 5.4]
size_t
qHashBits
(const
void
*
p
,
size_t
len
,
size_t
seed
= 0)
Returns the hash value for the memory block of size len pointed to by p ，使用 seed 做计算种子。
Use this function only to implement qHash () for your own custom types. For example, here's how you could implement a qHash () overload for std::vector<int>:
inline size_t qHash(const std::vector<int> &key, size_t seed = 0) { if (key.empty()) return seed; else return qHashBits(&key.front(), key.size() * sizeof(int), seed); }
This takes advantage of the fact that std::vector lays out its data contiguously. If that is not the case, or the contained type has padding, you should use qHashRange () 代替。
It bears repeating that the implementation of qHashBits() - like the qHash () overloads offered by Qt - may change at any time. You 不必 rely on the fact that qHashBits() will give the same results (for the same inputs) across different Qt versions.
该函数在 Qt 5.4 引入。
另请参阅 qHashRange () 和 qHashRangeCommutative ().
[since 6.0]
template <typename T>
size_t
qHashMulti
(
size_t
seed
, const
T
&...
args
)
返回哈希值为 args ，使用 seed to seed the calculation, by successively applying qHash () to each element and combining the hash values into a single one.
Note that the order of the arguments is significant. If order does not matter, use qHashMultiCommutative () instead. If you are hashing raw memory, use qHashBits (); if you are hashing a range, use qHashRange ().
This function is provided as a convenience to implement
qHash
() for your own custom types. For example, here's how you could implement a
qHash
() overload for a class
Employee
:
#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) { return e1.name() == e2.name() && e1.dateOfBirth() == e2.dateOfBirth(); } inline size_t qHash(const Employee &key, size_t seed) { return qHashMulti(seed, key.name(), key.dateOfBirth()); } #endif // EMPLOYEE_H
该函数在 Qt 6.0 引入。
另请参阅 qHashMultiCommutative and qHashRange .
[since 6.0]
template <typename T>
size_t
qHashMultiCommutative
(
size_t
seed
, const
T
&...
args
)
返回哈希值为 args ，使用 seed to seed the calculation, by successively applying qHash () to each element and combining the hash values into a single one.
The order of the arguments is insignificant. If order does matter, use qHashMulti () instead, as it may produce better quality hashing. If you are hashing raw memory, use qHashBits (); if you are hashing a range, use qHashRange ().
This function is provided as a convenience to implement qHash () for your own custom types.
该函数在 Qt 6.0 引入。
另请参阅 qHashMulti and qHashRange .
[since 5.5]
template <typename InputIterator>
size_t
qHashRange
(
InputIterator
first
,
InputIterator
last
,
size_t
seed
= 0)
Returns the hash value for the range [ first , last ), using seed to seed the calculation, by successively applying qHash () to each element and combining the hash values into a single one.
The return value of this function depends on the order of elements in the range. That means that
{0, 1, 2}
and
{1, 2, 0}
hash to different values. If order does not matter, for example for hash tables, use qHashRangeCommutative () instead. If you are hashing raw memory, use qHashBits ().
Use this function only to implement qHash () for your own custom types. For example, here's how you could implement a qHash () overload for std::vector<int>:
inline size_t qHash(const std::vector<int> &key, size_t seed = 0) { return qHashRange(key.begin(), key.end(), seed); }
It bears repeating that the implementation of qHashRange() - like the qHash () overloads offered by Qt - may change at any time. You 不必 rely on the fact that qHashRange() will give the same results (for the same inputs) across different Qt versions, even if qHash () for the element type would.
该函数在 Qt 5.5 引入。
另请参阅 qHashBits () 和 qHashRangeCommutative ().
[since 5.5]
template <typename InputIterator>
size_t
qHashRangeCommutative
(
InputIterator
first
,
InputIterator
last
,
size_t
seed
= 0)
Returns the hash value for the range [ first , last ), using seed to seed the calculation, by successively applying qHash () to each element and combining the hash values into a single one.
The return value of this function does not depend on the order of elements in the range. That means that
{0, 1, 2}
and
{1, 2, 0}
hash to the same values. If order matters, for example, for vectors and arrays, use qHashRange () instead. If you are hashing raw memory, use qHashBits ().
Use this function only to implement qHash () for your own custom types. For example, here's how you could implement a qHash () overload for std::unordered_set<int>:
inline size_t qHash(const std::unordered_set<int> &key, size_t seed = 0) { return qHashRangeCommutative(key.begin(), key.end(), seed); }
It bears repeating that the implementation of qHashRangeCommutative() - like the qHash () overloads offered by Qt - may change at any time. You 不必 rely on the fact that qHashRangeCommutative() will give the same results (for the same inputs) across different Qt versions, even if qHash () for the element type would.
该函数在 Qt 5.5 引入。
另请参阅 qHashBits () 和 qHashRange ().
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 .
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 .