Stores a weak pointer to a potentially shared object. More...

Public Typedefs
using	element_type = typename std::shared_ptr< T >::element_type

using	ElementType = element_type

using	pointer = element_type *

using	Pointer = pointer

Public Methods
	QWeakPointer ()

template<typename U >
	QWeakPointer (const QSharedPointer< U > &p)

	QWeakPointer (const QWeakPointer< T > &other)

template<typename U >
	QWeakPointer (const QWeakPointer< U > &other)

	QWeakPointer (QWeakPointer< T > &&other)

	QWeakPointer (T *p)

	~QWeakPointer ()

void	clear () noexcept

Pointer	data () const noexcept

bool	expired () const noexcept

bool	isNull () const

	operator bool () const noexcept

bool	operator! () const

template<typename U >
QWeakPointer &	operator= (const QSharedPointer< U > &p) noexcept

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

QWeakPointer &	operator= (QWeakPointer< T > &&other)

template<typename U >
bool	owner_before (const QSharedPointer< U > &p) const noexcept

template<typename U >
bool	owner_before (const QWeakPointer< U > &p) const noexcept

QSharedPointer< T >	toStrongRef () const noexcept

Related Functions
These are not member functions
bool	operator!= (const QSharedPointer< T1 > &ptr1, const QWeakPointer< T2 > &ptr2)

bool	operator!= (const QWeakPointer< T > &ptr1, std::nullptr_t)

bool	operator!= (const QWeakPointer< T1 > &ptr1, const QSharedPointer< T2 > &ptr2)

bool	operator!= (std::nullptr_t, const QWeakPointer< T > &ptr2)

bool	operator== (const QSharedPointer< T1 > &ptr1, const QWeakPointer< T2 > &ptr2)

bool	operator== (const QWeakPointer< T > &ptr1, std::nullptr_t)

bool	operator== (const QWeakPointer< T1 > &ptr1, const QSharedPointer< T2 > &ptr2)

bool	operator== (std::nullptr_t, const QWeakPointer< T > &ptr2)

Detailed Description

template<typename T>
class QWeakPointer< T >

The QWeakPointer class stores a weak pointer to a potentially shared object. A weak pointer is a smart pointer which does take ownership or manage the lifetime of the shared object. A CsWeakPointer can only be created by calling QSharedPointer::toWeakRef() or using the constructor in QWeakPointer which accepts a QSharedPointer.

To access the object which QWeakPointer points to, convert it to QSharedPointer and ensure the shared pointer is not a nullptr. If the shared pointer is not a nullptr, the object will not be deleted while the shared pointer is in scope.

QWeakPointer also provides a data() method which returns a raw pointer to the object. This method should only be used if your code can absolutely guarantee the object will not get deleted.

See also: QSharedPointer

Member Typedef Documentation

template<typename T >

QWeakPointer< T >::element_type

Typedef for std::weak_ptr<T>::element_type.

template<typename T >

QWeakPointer< T >::ElementType

Typedef for element_type.

template<typename T >

QWeakPointer< T >::pointer

Typedef for element_type *.

template<typename T >

QWeakPointer< T >::Pointer

Typedef for pointer.

Constructor & Destructor Documentation

template<typename T >

QWeakPointer< T >::QWeakPointer ( )

Creates a new QWeakPointer which contains a nullptr.

template<typename T >

template<typename U >

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

Creates a new QWeakPointer which points to the same object as other. This constructor is only available if U* can be converted to a T*.

template<typename T >

QWeakPointer< T >::QWeakPointer ( T * p )

Creates a new QWeakPointer which points to p. This constructor is only available if T is a class which inherits from QObject.

This constructor uses the internal shared pointer in QObject pointed to by p, to create the new weak pointer.

template<typename T >

QWeakPointer< T >::~QWeakPointer ( )

Destroys this QWeakPointer object. The pointer referenced by this object will not be deleted.

template<typename T >

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

Copy constructs a new QWeakPointer from other.

template<typename T >

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

Move constructs a new QWeakPointer from other.

template<typename T >

template<typename U >

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

Creates a new QWeakPointer which contains a weak reference to the shared pointer p.

Method Documentation

template<typename T >

void QWeakPointer< T >::clear ( )

noexcept

Sets this QWeakPointer object to a nullptr.

template<typename T >

Pointer QWeakPointer< T >::data ( ) const

noexcept

Returns the value of the raw pointer in this QWeakPointer. If the object has already been deleted this method will return a nullptr. Dereferencing this raw pointer is only permissible if the code can absolutely guarantee the object will not be deleted before the dereference occurs.

See also: toStrongRef()

template<typename T >

bool QWeakPointer< T >::expired ( ) const

noexcept

Equivalent to calling isNull().

template<typename T >

bool QWeakPointer< T >::isNull ( ) const

Returns true if this object contains a reference to a null pointer. Since the object the QWeakPointer references can be deleted at any time, a value of true does not guarantee the object is still alive after calling this method.

template<typename T >

QWeakPointer< T >::operator bool ( ) const

explicitnoexcept

Returns true if the current QWeakPointer is not a nullptr. This method is called when a shared pointer is used in an "if statement" or another context where a boolean value is expected. Since this method is explicit it is not possible to assign a QSharedPointer to a boolean.

// example 1
if (myWeakPtr) {
   // ...
}
 
// example 2
bool isTest_A = myWeakPtr;                      // will *not* compile
 
bool isTest_B = (myWeakPtr != nullptr);         // compiles, valid code
 
bool isTest_C = bool(myWeakPtr);                // compiles, valid code

template<typename T >

bool QWeakPointer< T >::operator! ( ) const

Returns true if this object is a nullptr. This method is called when a shared pointer is used in an "if statement" or another context where a boolean value is expected.

if (! myWeakPtr) {
   // ...
}

template<typename T >

template<typename U >

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

noexcept

Copy assigns from the shared pointer p and returns a reference to this object.

template<typename T >

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

Copy assigns from other and returns a reference to this object.

template<typename T >

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

Move assigns from other and returns a reference to this object.

template<typename T >

template<typename U >

bool QWeakPointer< T >::owner_before ( const QSharedPointer & p ) const

noexcept

Returns true if the current pointer is less than p, otherwise returns false.

template<typename T >

template<typename U >

bool QWeakPointer< T >::owner_before ( const QWeakPointer & p ) const

noexcept

Returns true if the current pointer is less than p, otherwise returns false.

template<typename T >

QSharedPointer< T > QWeakPointer< T >::toStrongRef ( ) const

noexcept

Converts the current weak pointer to a shared pointer and returns the QSharedPointer. This method can fail if the object the QWeakPointer is pointing to has been deleted. To prevent undefined behavior verify the return value by calling QSharedPointer::isNull() before dereferencing.

QWeakPointer<int> weakPtr;
QSharedPointer<int> ptr = weakPtr.toStrongRef();
 
if (ptr != nullptr) {
   qDebug() << "Pointer is valid and points to an existing object";
}

See also: QSharedPointer::QSharedPointer()

Friends And Related Function Documentation

bool operator!=	(	const QSharedPointer< T1 > &	ptr1,
		const QWeakPointer< T2 > &	ptr2
	)

bool operator!=	(	const QWeakPointer< T > &	ptr1,
		std::nullptr_t
	)

bool operator!=	(	const QWeakPointer< T1 > &	ptr1,
		const QSharedPointer< T2 > &	ptr2
	)

bool operator!=	(	std::nullptr_t	,
		const QWeakPointer< T > &	ptr2
	)

bool operator==	(	const QSharedPointer< T1 > &	ptr1,
		const QWeakPointer< T2 > &	ptr2
	)

bool operator==	(	const QWeakPointer< T > &	ptr1,
		std::nullptr_t
	)

bool operator==	(	const QWeakPointer< T1 > &	ptr1,
		const QSharedPointer< T2 > &	ptr2
	)

bool operator==	(	std::nullptr_t	,
		const QWeakPointer< T > &	ptr2
	)

Public Typedefs

Public Methods

Related Functions

Detailed Description

template<typename T> class QWeakPointer< T >

Member Typedef Documentation

Constructor & Destructor Documentation

Method Documentation

Friends And Related Function Documentation

template<typename T>
class QWeakPointer< T >