The QHash class is a template class that provides a hash-table-based dictionary. More...
Header: | #include <QHash> |
qmake: | QT += core |
Inherited By: |
Note: All functions in this class are reentrant.
class | const_iterator |
class | iterator |
class | key_iterator |
typedef | ConstIterator |
typedef | Iterator |
typedef | const_key_value_iterator |
typedef | difference_type |
typedef | key_type |
typedef | key_value_iterator |
typedef | mapped_type |
typedef | size_type |
QHash() | |
QHash(int) | |
QHash(const QHash<K, V> &other) | |
QHash(QHash<K, V> &&other) | |
~QHash() | |
QHash::iterator | begin() |
QHash::const_iterator | begin() const |
int | 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 |
int | count(const Key &key) const |
int | count() const |
bool | empty() const |
QHash::iterator | end() |
QHash::const_iterator | end() const |
QPair<QHash::iterator, QHash::iterator> | equal_range(const Key &key) |
QPair<QHash::const_iterator, QHash::const_iterator> | equal_range(const Key &key) const |
QHash::iterator | erase(QHash::const_iterator pos) |
QHash::iterator | erase(QHash::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) |
QHash::iterator | insertMulti(const Key &key, const T &value) |
bool | isEmpty() const |
const Key | key(const T &value) const |
const Key | key(const T &value, const Key &defaultKey) 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 |
int | remove(const Key &key) |
void | reserve(int size) |
int | size() const |
void | squeeze() |
void | swap(QHash<K, V> &other) |
T | take(const Key &key) |
QList<Key> | uniqueKeys() const |
QHash<K, V> & | unite(const QHash<K, V> &other) |
const T | value(const Key &key) const |
const T | value(const Key &key, const T &defaultValue) const |
QList<T> | values() const |
QList<T> | values(const Key &key) const |
bool | operator!=(const QHash<K, V> &other) const |
QHash<K, V> & | operator=(const QHash<K, V> &other) |
QHash<K, V> & | operator=(QHash<K, V> &&other) |
bool | operator==(const QHash<K, V> &other) const |
T & | operator[](const Key &key) |
const T | operator[](const Key &key) const |
int | qGlobalQHashSeed() |
uint | qHash(char key, uint seed = ...) |
uint | qHash(const QUrl &url, uint seed = 0) |
uint | qHash(const QDateTime &key, uint seed = ...) |
uint | qHash(const QDate &key, uint seed = ...) |
uint | qHash(const QTime &key, uint seed = ...) |
uint | qHash(const QPair<T1, T2> &key, uint seed = ...) |
uint | qHash(const int &key, uint seed = ...) |
uint | qHash(uchar key, uint seed = ...) |
uint | qHash(signed char key, uint seed = ...) |
uint | qHash(ushort key, uint seed = ...) |
uint | qHash(short key, uint seed = ...) |
uint | qHash(uint key, uint seed = ...) |
uint | qHash(int key, uint seed = ...) |
uint | qHash(ulong key, uint seed = ...) |
uint | qHash(long key, uint seed = ...) |
uint | qHash(quint64 key, uint seed = ...) |
uint | qHash(qint64 key, uint seed = ...) |
uint | qHash(float key, uint seed = 0) |
uint | qHash(double key, uint seed = 0) |
uint | qHash(long double key, uint seed = 0) |
uint | qHash(const QChar key, uint seed = ...) |
uint | qHash(const QByteArray &key, uint seed = ...) |
uint | qHash(const QBitArray &key, uint seed = ...) |
uint | qHash(const QString &key, uint seed = ...) |
uint | qHash(const QStringRef &key, uint seed = ...) |
uint | qHash(QLatin1String key, uint seed = ...) |
uint | qHash(const T *key, uint seed = ...) |
uint | qHash(const QHash<Key, T> &key, uint seed = ...) |
uint | qHash(const QSet<T> &key, uint seed = ...) |
uint | qHash(const QVersionNumber &key, uint seed = 0) |
qHash(QSslEllipticCurve curve, uint seed) | |
qHash(const QSslCertificate &key, uint seed) | |
qHash(const QSslError &key, uint seed) | |
uint | qHashBits(const void *p, int len, uint seed = ...) |
uint | qHashRange(InputIterator first, InputIterator last, uint seed = ...) |
uint | qHashRangeCommutative(InputIterator first, InputIterator last, uint seed = ...) |
void | qSetGlobalQHashSeed(int newSeed) |
QDataStream & | operator<<(QDataStream &out, const QHash<Key, T> &hash) |
QDataStream & | operator>>(QDataStream &in, QHash<Key, T> &hash) |
The QHash class is a template class that provides a hash-table-based dictionary.
QHash<Key, T> is one of Qt's generic container classes. It stores (key, value) pairs and provides very fast lookup of the value associated with a key.
QHash provides very similar functionality to QMap. The differences are:
Here's an example QHash with QString keys and int
values:
QHash<QString, int> hash;
To insert a (key, value) pair into the hash, you can use 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);
To look up a value, use operator[]() or 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 default-constructed value.
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() and 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 << endl; }
To avoid this problem, replace hash[i]
with hash.value(i)
in the code above.
Internally, QHash uses a hash table to perform lookups. Unlike Qt 3's QDict
class, which needed to be initialized with a prime number, QHash's hash table automatically grows and shrinks 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.
If you want to navigate through all the (key, value) pairs stored in a QHash, you can use an iterator. QHash provides both Java-style iterators (QHashIterator and QMutableHashIterator) and STL-style iterators (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() << 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() << 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.
Normally, 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
However, you can store multiple values per key by using insertMulti() instead of insert() (or using the convenience subclass QMultiHash). If you want to retrieve all the values for a single key, you can use values(const Key &key), which returns a QList<T>:
QList<int> values = hash.values("plenty"); for (int i = 0; i < values.size(); ++i) cout << values.at(i) << endl;
The items that share the same key are available from most recently to least recently inserted. A more efficient approach is to call find() to get the iterator for the first item with a key and iterate from there:
QHash<QString, int>::iterator i = hash.find("plenty"); while (i != hash.end() && i.key() == "plenty") { cout << i.value() << endl; ++i; }
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 << 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's key and value data types must be assignable data types. You cannot, for example, store a QWidget as a value; instead, store a 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 qHash() function in the type's namespace that returns a hash value for an argument of the key's type.
The qHash() 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
, then qHash(e1) == qHash(e2)
must hold as well. However, to obtain good performance, the qHash() function should attempt to return different hash values
for different keys to the largest extent possible.
For a key type K
, the qHash function must have one of these signatures:
uint qHash(K key); uint qHash(const K &key); uint qHash(K key, uint seed); uint qHash(const K &key, uint 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).
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, and 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 qHash() implementation.
Example:
#ifndef EMPLOYEE_H #define EMPLOYEE_H class Employee { public: Employee() {} Employee(const QString &name, const 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 uint qHash(const Employee &key, uint seed) { return qHash(key.name(), seed) ^ key.dateOfBirth().day(); } #endif // EMPLOYEE_H
In the example above, we've relied on Qt's global qHash(const QString &, uint) to give us a hash value for the employee's name, and XOR'ed this with the day they were born to help produce unique hashes for people with the same name.
Note that the implementation of the qHash() overloads offered by Qt may change at any time. You must not 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 Algorithmic Complexity 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() function.
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 qSetGlobalQHashSeed() function with the value 0.
See also QHashIterator, QMutableHashIterator, QMap, and QSet.
Qt-style synonym for QHash::const_iterator.
Qt-style synonym for QHash::iterator.
The QMap::const_key_value_iterator typedef provides an STL-style const iterator for QHash and QMultiHash.
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.
This typedef was introduced in Qt 5.10.
See also QKeyValueIterator.
Typedef for ptrdiff_t. Provided for STL compatibility.
Typedef for Key. Provided for STL compatibility.
The QMap::key_value_iterator typedef provides an STL-style iterator for QHash and QMultiHash.
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.
This typedef was introduced in Qt 5.10.
See also QKeyValueIterator.
Typedef for T. Provided for STL compatibility.
Typedef for int. Provided for STL compatibility.
Constructs an empty hash.
See also clear().
Constructs a hash with a copy of each of the elements in the initializer list list.
This function is only available if the program is being compiled in C++11 mode.
This function was introduced in Qt 5.1.
Constructs a copy of other.
This operation occurs in constant time, because QHash is implicitly shared. 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 linear time.
See also operator=().
Move-constructs a QHash instance, making it point at the same object that other was pointing to.
This function was introduced in Qt 5.2.
Destroys the hash. References to the values in the hash and all iterators of this hash become invalid.
Returns an STL-style iterator pointing to the first item in the hash.
See also constBegin() and end().
This is an overloaded function.
Returns the number of buckets in the QHash's internal hash table.
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().
See also reserve() and squeeze().
Returns a const STL-style iterator pointing to the first item in the hash.
This function was introduced in Qt 5.0.
Returns a const STL-style iterator pointing to the imaginary item after the last item in the hash.
This function was introduced in Qt 5.0.
Removes all items from the hash.
See also remove().
Returns a const STL-style iterator pointing to the first item in the hash.
See also begin() and constEnd().
Returns a const STL-style iterator pointing to the imaginary item after the last item in the hash.
See also constBegin() and end().
Returns an iterator pointing to the item with the key in the hash.
If the hash contains no item with the key, the function returns constEnd().
This function was introduced in Qt 4.1.
See also find() and QMultiHash::constFind().
Returns a const STL-style iterator pointing to the first entry in the hash.
This function was introduced in Qt 5.10.
See also keyValueBegin().
Returns a const STL-style iterator pointing to the imaginary entry after the last entry in the hash.
This function was introduced in Qt 5.10.
See also constKeyValueBegin().
Returns true
if the hash contains an item with the key; otherwise returns false
.
See also count() and QMultiHash::contains().
Returns the number of items associated with the key.
See also contains() and insertMulti().
This is an overloaded function.
Same as size().
This function is provided for STL compatibility. It is equivalent to isEmpty(), returning true if the hash is empty; otherwise returns false
.
Returns an STL-style iterator pointing to the imaginary item after the last item in the hash.
See also begin() and constEnd().
This is an overloaded function.
Returns a pair of iterators delimiting the range of values [first, second)
, that are stored under key. If the range is empty then both iterators will be equal to end().
This function was introduced in Qt 5.7.
This is an overloaded function.
This function was introduced in Qt 5.7.
Removes the (key, value) pair associated with the iterator pos from the hash, and returns an iterator to the next item in the hash.
Unlike remove() and take(), this function never causes 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; } }
This function was introduced in Qt 5.7.
See also remove(), take(), and find().
This is an overloaded function.
Returns an iterator pointing to the item with the key in the hash.
If the hash contains no item with the key, the function returns 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() << endl; ++i; }
See also value(), values(), and QMultiHash::find().
This is an overloaded function.
Inserts a new item with the key and a value of value.
If there is already an item with the key, that item's value is replaced with value.
If there are multiple items with the key, the most recently inserted item's value is replaced with value.
See also insertMulti().
Inserts a new item with the key and a value of value.
If there is already an item with the same key in the hash, this function will simply create a new one. (This behavior is different from insert(), which overwrites the value of an existing item.)
See also insert() and values().
Returns true
if the hash contains no items; otherwise returns false.
See also size().
Returns the first key mapped to value.
If the hash contains no item with the value, the function returns a default-constructed key.
This function can be slow (linear time), because QHash's internal data structure is optimized for fast lookup by key, not by value.
This is an overloaded function.
Returns the first key mapped to value, or defaultKey if the hash contains no item mapped to value.
This function can be slow (linear time), because QHash's internal data structure is optimized for fast lookup by key, not by value.
This function was introduced in Qt 4.3.
Returns a const STL-style iterator pointing to the first key in the hash.
This function was introduced in Qt 5.6.
See also keyEnd().
Returns a const STL-style iterator pointing to the imaginary item after the last key in the hash.
This function was introduced in Qt 5.6.
See also keyBegin().
Returns an STL-style iterator pointing to the first entry in the hash.
This function was introduced in Qt 5.10.
See also keyValueEnd().
Returns a const STL-style iterator pointing to the first entry in the hash.
This function was introduced in Qt 5.10.
See also keyValueEnd().
Returns an STL-style iterator pointing to the imaginary entry after the last entry in the hash.
This function was introduced in Qt 5.10.
See also keyValueBegin().
Returns a const STL-style iterator pointing to the imaginary entry after the last entry in the hash.
This function was introduced in Qt 5.10.
See also keyValueBegin().
Returns a list containing all the keys in the hash, in an arbitrary order. Keys that occur multiple times in the hash (because items were inserted with insertMulti(), or unite() was used) also occur multiple times in the list.
To obtain a list of unique keys, where each key from the map only occurs once, use uniqueKeys().
The order is guaranteed to be the same as that used by values().
See also uniqueKeys(), values(), and key().
This is an overloaded function.
Returns a list containing all the keys associated with value value, in an arbitrary order.
This function can be slow (linear time), because QHash's internal data structure is optimized for fast lookup by key, not by value.
Removes all the items that have the key from the hash. Returns the number of items removed which is usually 1 but will be 0 if the key isn't in the hash, or greater than 1 if insertMulti() has been used with the key.
See also clear(), take(), and QMultiHash::remove().
Ensures that the QHash's internal hash table consists of at least size buckets.
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 slightly more than the maximum number of items expected in the hash. size doesn't have to be prime, because QHash will use a prime number internally anyway. 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 shrinks or grows to provide good performance without wasting too much memory.
See also squeeze() and capacity().
Returns the number of items in the hash.
See also isEmpty() and count().
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.
See also reserve() and capacity().
Swaps hash other with this hash. This operation is very fast and never fails.
This function was introduced in Qt 4.8.
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 default-constructed value. If there are multiple items for key in the hash, only the most recently inserted one is removed.
If you don't use the return value, remove() is more efficient.
See also remove().
Returns a list containing all the keys in the map. Keys that occur multiple times in the map (because items were inserted with insertMulti(), or unite() was used) occur only once in the returned list.
This function was introduced in Qt 4.2.
Inserts all the items in the other hash into this hash. If a key is common to both hashes, the resulting hash will contain the key multiple times.
See also insertMulti().
Returns the value associated with the key.
If the hash contains no item with the key, the function returns a default-constructed value. If there are multiple items for the key in the hash, the value of the most recently inserted one is returned.
See also key(), values(), contains(), and operator[]().
This is an overloaded function.
If the hash contains no item with the given key, the function returns defaultValue.
Returns a list containing all the values in the hash, in an arbitrary order. If a key is associated with multiple values, all of its values will be in the list, and not just the most recently inserted one.
The order is guaranteed to be the same as that used by keys().
This is an overloaded function.
Returns a list of all the values associated with the key, from the most recently inserted to the least recently inserted.
See also count() and insertMulti().
Returns true
if other is not 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==()
.
See also operator==().
Assigns other to this hash and returns a reference to this hash.
Move-assigns other to this QHash instance.
This function was introduced in Qt 5.2.
Returns 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==()
.
See also operator!=().
Returns the value associated with the key as a modifiable reference.
If the hash contains no item with the key, the function inserts a default-constructed value into the hash with the key, and returns a reference to it. If the hash contains multiple items with the key, this function returns a reference to the most recently inserted value.
See also insert() and value().
This is an overloaded function.
Same as value().
Returns the current global QHash seed.
The seed is set in any newly created QHash. See qHash about how this seed is being used by QHash.
This function was introduced in Qt 5.6.
See also qSetGlobalQHashSeed.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the url. If specified, seed is used to initialize the hash.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
Types T1
and T2
must be supported by qHash().
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
Types T1
and T2
must be supported by qHash().
Note: The return type of this function is not the same as that of
qHash(qMakePair(key.first, key.second), seed);
The two functions use different hashing algorithms; due to binary compatibility constraints, we cannot change the QPair algorithm to match the std::pair one before Qt 6.
This function was introduced in Qt 5.7.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.3.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.3.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.3.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.0.
Returns the hash value for the key, using seed to seed the calculation.
Type T
must be supported by qHash().
This function was introduced in Qt 5.8.
Returns the hash value for the key, using seed to seed the calculation.
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.
This function was introduced in Qt 5.5.
Returns the hash value for the key, using seed to seed the calculation.
This function was introduced in Qt 5.6.
This function was introduced in Qt 5.5.
This function was introduced in Qt 5.4.
This function was introduced in Qt 5.4.
Returns the hash value for the memory block of size len pointed to by p, using seed to seed the calculation.
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 uint qHash(const std::vector<int> &key, uint 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() instead.
It bears repeating that the implementation of qHashBits() - like the qHash() overloads offered by Qt - may change at any time. You must not rely on the fact that qHashBits() will give the same results (for the same inputs) across different Qt versions.
This function was introduced in Qt 5.4.
See also qHashRange() and qHashRangeCommutative().
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 uint qHash(const std::vector<int> &key, uint 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 must not 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.
This function was introduced in Qt 5.5.
See also qHashBits() and qHashRangeCommutative().
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 uint qHash(const std::unordered_set<int> &key, uint 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 must not 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.
This function was introduced in Qt 5.5.
See also qHashBits() and qHashRange().
Sets the global QHash seed to newSeed.
Manually setting the global QHash seed value should be done only for testing and debugging purposes, when deterministic and reproducible behavior on a QHash is needed. We discourage to do it in production code as it can make your application susceptible to algorithmic complexity attacks.
From Qt 5.10 and onwards, the only allowed values are 0 and -1. Passing the value -1 will reinitialize the global QHash seed to a random value, while the value of 0 is used to request a
stable algorithm for C++ primitive types types (like int
) and string types (QString, QByteArray).
The seed is set in any newly created QHash. See qHash about how this seed is being used by QHash.
If the environment variable QT_HASH_SEED
is set, calling this function will result in a no-op.
This function was introduced in Qt 5.6.
See also qGlobalQHashSeed.
Writes the hash hash to stream out.
This function requires the key and value types to implement operator<<()
.
See also Serializing Qt Data Types.
Reads a hash from stream in into hash.
This function requires the key and value types to implement operator>>()
.
See also Serializing Qt Data Types.