QSharedPointer Class

Member Function Documentation

QSharedPointer::QSharedPointer()

Creates a QSharedPointer that points to null (0).

QSharedPointer::QSharedPointer(X *ptr)

Creates a QSharedPointer that points to ptr. The pointer ptr becomes managed by this QSharedPointer and must not be passed to another QSharedPointer object or deleted outside this object.

Since Qt 5.8, when the last reference to this QSharedPointer gets destroyed, ptr will be deleted by calling X's destructor (even if X is not the same as QSharedPointer's template parameter T). Previously, the destructor for T was called.

QSharedPointer::QSharedPointer(X *ptr, Deleter d)

Creates a QSharedPointer that points to ptr. The pointer ptr becomes managed by this QSharedPointer and must not be passed to another QSharedPointer object or deleted outside this object.

The deleter parameter d specifies the custom deleter for this object. The custom deleter is called, instead of the operator delete(), when the strong reference count drops to 0. This is useful, for instance, for calling deleteLater() on a QObject instead:

static void doDeleteLater(MyObject *obj)
{
    obj->deleteLater();
}

void otherFunction()
{
    QSharedPointer<MyObject> obj =
        QSharedPointer<MyObject>(new MyObject, doDeleteLater);

    // continue using obj
    obj.clear();    // calls obj->deleteLater();
}

Note that the custom deleter function will be called with a pointer to type X, even if the QSharedPointer template parameter T is not the same.

It is also possible to specify a member function directly, as in:

QSharedPointer<MyObject> obj =
    QSharedPointer<MyObject>(new MyObject, &QObject::deleteLater);

See also clear().

QSharedPointer::QSharedPointer(int)

Default constructs an instance of QSharedPointer.

QSharedPointer::QSharedPointer(int, Deleter d)

Creates a QSharedPointer that is null. This is equivalent to the QSharedPointer default constructor.

The deleter parameter d specifies the custom deleter for this object. The custom deleter is called, instead of the operator delete(), when the strong reference count drops to 0.

This function was introduced in Qt 5.8.

QSharedPointer::QSharedPointer(const QSharedPointer<T> &other)

Creates a QSharedPointer object that shares other's pointer.

If T is a derived type of the template parameter of this class, QSharedPointer will perform an automatic cast. Otherwise, you will get a compiler error.

QSharedPointer::QSharedPointer(const QWeakPointer<T> &other)

Creates a QSharedPointer by promoting the weak reference other to strong reference and sharing its pointer.

If T is a derived type of the template parameter of this class, QSharedPointer will perform an automatic cast. Otherwise, you will get a compiler error.

See also QWeakPointer::toStrongRef().

QSharedPointer::~QSharedPointer()

Destroys this QSharedPointer object. If it is the last reference to the pointer stored, this will delete the pointer as well.

void QSharedPointer::clear()

Clears this QSharedPointer object, dropping the reference that it may have had to the pointer. If this was the last reference, then the pointer itself will be deleted.

QSharedPointer<X> QSharedPointer::constCast() const

Performs a const_cast from this pointer's type to X and returns a QSharedPointer that shares the reference. This function can be used for up- and for down-casting, but is more useful for up-casting.

See also isNull() and qSharedPointerConstCast().

[static] QSharedPointer<T> QSharedPointer::create()

Creates a QSharedPointer object and allocates a new item of type T. The QSharedPointer internals and the object are allocated in one single memory allocation, which could help reduce memory fragmentation in a long-running application.

This function calls the default constructor for type T.

This function was introduced in Qt 5.1.

[static] QSharedPointer<T> QSharedPointer::create(...)

This is an overloaded function.

Creates a QSharedPointer object and allocates a new item of type T. The QSharedPointer internals and the object are allocated in one single memory allocation, which could help reduce memory fragmentation in a long-running application.

This function will attempt to call a constructor for type T that can accept all the arguments passed. Arguments will be perfectly-forwarded.

Note: This function is only fully available with a C++11 compiler that supports perfect forwarding of an arbitrary number of arguments.

If the compiler does not support the necessary C++11 features, then a restricted version is available since Qt 5.4: you may pass one (but just one) argument, and it will always be passed by const reference.

If you target Qt before version 5.4, you must use the overload that calls the default constructor.

This function was introduced in Qt 5.1.

T *QSharedPointer::data() const

Returns the value of the pointer referenced by this object.

Note: do not delete the pointer returned by this function or pass it to another function that could delete it, including creating QSharedPointer or QWeakPointer objects.

QSharedPointer<X> QSharedPointer::dynamicCast() const

Performs a dynamic cast from this pointer's type to X and returns a QSharedPointer that shares the reference. If this function is used to up-cast, then QSharedPointer will perform a dynamic_cast, which means that if the object being pointed by this QSharedPointer is not of type X, the returned object will be null.

Note: the template type X must have the same const and volatile qualifiers as the template of this object, or the cast will fail. Use constCast() if you need to drop those qualifiers.

See also qSharedPointerDynamicCast().

T *QSharedPointer::get() const

Same as data().

This function is provided for API compatibility with std::shared_ptr.

This function was introduced in Qt 5.11.

bool QSharedPointer::isNull() const

Returns true if this object is holding a reference to a null pointer.

QSharedPointer<X> QSharedPointer::objectCast() const

Performs a qobject_cast() from this pointer's type to X and returns a QSharedPointer that shares the reference. If this function is used to up-cast, then QSharedPointer will perform a qobject_cast, which means that if the object being pointed by this QSharedPointer is not of type X, the returned object will be null.

Note: the template type X must have the same const and volatile qualifiers as the template of this object, or the cast will fail. Use constCast() if you need to drop those qualifiers.

This function was introduced in Qt 4.6.

See also qSharedPointerObjectCast().

void QSharedPointer::reset()

Same as clear(). For std::shared_ptr compatibility.

This function was introduced in Qt 5.0.

void QSharedPointer::reset(T *t)

Resets this QSharedPointer object to point to t instead. Equivalent to:

QSharedPointer<T> other(t); this->swap(other);

This function was introduced in Qt 5.0.

void QSharedPointer::reset(T *t, Deleter deleter)

Resets this QSharedPointer object to point to t instead, with the Deleter deleter. Equivalent to:

QSharedPointer<T> other(t, deleter); this->swap(other);

This function was introduced in Qt 5.0.

QSharedPointer<X> QSharedPointer::staticCast() const

Performs a static cast from this pointer's type to X and returns a QSharedPointer that shares the reference. This function can be used for up- and for down-casting, but is more useful for up-casting.

Note: the template type X must have the same const and volatile qualifiers as the template of this object, or the cast will fail. Use constCast() if you need to drop those qualifiers.

See also dynamicCast(), constCast(), and qSharedPointerCast().

void QSharedPointer::swap(QSharedPointer<T> &other)

Swaps this shared pointer instance with other. This function is very fast and never fails.

This function was introduced in Qt 5.3.

QWeakPointer<T> QSharedPointer::toWeakRef() const

Returns a weak reference object that shares the pointer referenced by this object.

See also QWeakPointer::QWeakPointer().

bool QSharedPointer::operator bool() const

Returns true if this object is not null. This function is suitable for use in if-constructs, like:

if (sharedptr) { ... }

See also isNull().

bool QSharedPointer::operator!() const

Returns true if this object is null. This function is suitable for use in if-constructs, like:

if (!sharedptr) { ... }

See also isNull().

T &QSharedPointer::operator*() const

Provides access to the shared pointer's members.

See also isNull().

T *QSharedPointer::operator->() const

Provides access to the shared pointer's members.

See also isNull().

QSharedPointer<T> &QSharedPointer::operator=(const QSharedPointer<T> &other)

Makes this object share other's pointer. The current pointer reference is discarded and, if it was the last, the pointer will be deleted.

If T is a derived type of the template parameter of this class, QSharedPointer will perform an automatic cast. Otherwise, you will get a compiler error.

QSharedPointer<T> &QSharedPointer::operator=(const QWeakPointer<T> &other)

Promotes other to a strong reference and makes this object share a reference to the pointer referenced by it. The current pointer reference is discarded and, if it was the last, the pointer will be deleted.

If T is a derived type of the template parameter of this class, QSharedPointer will perform an automatic cast. Otherwise, you will get a compiler error.