QSet Class

template <typename T> class QSet

The QSet class is a template class that provides a hash-table-based set. More…

List of all members, including inherited members

Public Types

Public Functions

Detailed Description

QSet<T> stores unique values and tests for membership in constant time on average. The values are kept in no particular order. The value type needs operator== and either a qHash() overload or a std::hash specialization.

QSet<QString> names;
names << "Alice" << "Bob";
names.insert("Alice"); // already present, no change
bool hasBob = names.contains("Bob");

See also QHash and QSetIterator.

Differences from Qt

Member Type Documentation

typedef QSet::const_iterator

The constant iterator type.

typedef QSet::Container

The underlying std::unordered_set type used for storage.

typedef QSet::iterator

The iterator type. It is constant, so the values of a set cannot be modified through it.

typedef QSet::value_type

The type of the values stored in the set, T.

Member Function Documentation

QSet::QSet()

Constructs an empty set.

QSet::QSet(std::initializer_list<T> l)

This is an overloaded function.

Constructs a set with the values in the initializer list l.

template <typename It, typename = typename std::iterator_traits<It>::iterator_category>QSet::QSet(It first, It last)

This is an overloaded function.

Constructs a set with the values in the range from first up to, but not including, last.

const_iterator QSet::begin() const

Returns a constant iterator to the first value in the set.

See also end() and constBegin().

qsizetype QSet::capacity() const

Returns the number of buckets in the hash table of the set.

See also reserve() and squeeze().

const_iterator QSet::cbegin() const

Returns a constant iterator to the first value in the set; the same as begin().

const_iterator QSet::cend() const

Returns a constant iterator to the position after the last value in the set; the same as end().

void QSet::clear()

Removes all values from the set.

See also remove().

const_iterator QSet::constBegin() const

Returns a constant iterator to the first value in the set; the same as begin().

const_iterator QSet::constEnd() const

Returns a constant iterator to the position after the last value in the set; the same as end().

const_iterator QSet::constFind(const T &value) const

Returns an iterator to the value value, or constEnd() if the set does not contain it.

See also find() and contains().

bool QSet::contains(const T &t) const

Returns true if the set contains the value t; otherwise returns false.

See also insert() and find().

bool QSet::contains(const QSet &other) const

This is an overloaded function.

Returns true if the set contains every value of the set other; otherwise returns false.

qsizetype QSet::count() const

Returns the number of values in the set; the same as size().

bool QSet::empty() const

Returns true if the set has no values. Provided for compatibility with the standard library.

See also isEmpty().

const_iterator QSet::end() const

Returns a constant iterator to the position after the last value in the set.

See also begin() and constEnd().

iterator QSet::erase(const_iterator it)

Removes the value that it points to and returns an iterator to the value that followed it.

See also remove().

iterator QSet::find(const T &t) const

Returns an iterator to the value t, or end() if the set does not contain it.

See also contains().

iterator QSet::insert(const T &t)

Inserts the value t into the set if it is not already present, and returns an iterator to the value in the set.

See also remove() and contains().

QSet & QSet::intersect(const QSet &o)

Removes all values from this set that are not in the set o, and returns a reference to this set.

See also unite(), subtract() and intersects().

bool QSet::intersects(const QSet &o) const

Returns true if this set and the set o have at least one value in common; otherwise returns false.

See also intersect().

bool QSet::isEmpty() const

Returns true if the set contains no values; otherwise returns false.

See also size().

bool QSet::isSubsetOf(const QSet &other) const

Returns true if every value of this set is also in other.

This function was introduced in 5.12.

See also contains() and intersects().

QSet & QSet::operator&=(const QSet &o)

Removes all values from this set that are not in the set o, and returns a reference to this set; the same as intersect().

QSet & QSet::operator+=(const T &t)

This is an overloaded function.

Inserts the value t into the set and returns a reference to this set.

QSet & QSet::operator+=(const QSet &o)

This is an overloaded function.

Inserts all values of the set o into this set; the same as unite().

QSet & QSet::operator-=(const QSet &o)

Removes all values of the set o from this set and returns a reference to this set; the same as subtract().

QSet & QSet::operator<<(const T &t)

Inserts the value t into the set and returns a reference to this set; the same as insert(). The calls can be chained.

QSet & QSet::operator|=(const QSet &o)

Inserts all values of the set o into this set and returns a reference to this set; the same as unite().

bool QSet::remove(const T &t)

Removes the value t from the set. Returns true if the value was present; otherwise returns false.

See also insert() and clear().

template <typename Pred>qsizetype QSet::removeIf(Pred p)

Removes all values for which p returns true and returns the number of values removed. The predicate is called with an iterator to the value.

See also remove().

void QSet::reserve(qsizetype n)

Prepares the set for holding at least n values without rehashing.

qsizetype QSet::size() const

Returns the number of values in the set.

See also isEmpty() and count().

void QSet::squeeze()

Shrinks the hash table to the smallest size that holds the values.

See also capacity().

QSet & QSet::subtract(const QSet &o)

Removes all values of the set o from this set and returns a reference to this set.

See also unite() and intersect().

QList<T> QSet::toList() const

Returns the values of the set as a QList; the same as values().

QSet & QSet::unite(const QSet &o)

Inserts all values of the set o into this set and returns a reference to this set.

See also intersect() and subtract().

QList<T> QSet::values() const

Returns the values of the set as a QList, in unspecified order.

See also toList().