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These rights are described in the Trolltech GPL ** Exception version 1.0, which can be found at ** http://www.trolltech.com/products/qt/gplexception/ and in the file ** GPL_EXCEPTION.txt in this package. ** ** In addition, as a special exception, Trolltech, as the sole copyright ** holder for Qt Designer, grants users of the Qt/Eclipse Integration ** plug-in the right for the Qt/Eclipse Integration to link to ** functionality provided by Qt Designer and its related libraries. ** ** Trolltech reserves all rights not expressly granted herein. ** ** Trolltech ASA (c) 2007 ** ** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. ** ****************************************************************************/ #include /*! \class QSharedData \brief The QSharedData class is a base class for shared data objects. \reentrant \ingroup misc QSharedData is designed to be used together with QSharedDataPointer to implement custom \l{implicitly shared} classes. It provides thread-safe reference counting. See the QSharedDataPointer documentation for details. */ /*! \fn QSharedData::QSharedData() Constructs a QSharedData object with a reference count of 0. */ /*! \fn QSharedData::QSharedData(const QSharedData &other) Constructs a QSharedData object with a reference count of 0. (\a other is ignored.) */ /*! \class QSharedDataPointer \brief The QSharedDataPointer class provides a pointer to a shared data object. \reentrant \ingroup misc \mainclass QSharedDataPointer\ makes it easier to write your own implicitly shared classes. It handles reference counting behind the scenes in a thread-safe manner, ensuring that classes that use it can be \l{reentrant}. Implicit sharing is used throughout Qt to combine the memory and speed efficiency of pointers with the ease of use of value types. See the \l{Shared Classes} page for more information. Let's suppose that you want to make an \c Employee class implicitly shared. The procedure is: \list \o Define the \c Employee class with a single data member variable of type QSharedDataPointer<\c{EmployeeData}>. \o Define an \c EmployeeData class that derives from \l QSharedData and that contains all the variables that you would normally put in \c Employee. \endlist To show how this works in practice, we will review the entire source code for an implicitly shared \c Employee class. Here's the header file that defines the \c Employee class: \include snippets/sharedemployee/employee.h All accesses to the data in the setter and getter functions are made through the QSharedDataPointer object \c d. For non-const functions, operator->() automatically calls detach(), ensuring that modifications to one \c Employee object don't affect other \c Employee objects. The \c EmployeeData type is a simple class that inherits QSharedData and that provides a default constructor, a copy constructor, and a destructor. Normally, this is all you need in the "data" class. Here's the implementation of the \c EmployeeData members: \quotefromfile snippets/sharedemployee/employee.cpp \skipto ::EmployeeData() \printuntil /^\}/ \printline ::EmployeeData(const \printuntil /^\}/ \printline ::~EmployeeData \printuntil /^\}/ Let's now see how to implement the \c Employee constructors: \printline ::Employee() \printuntil } In the default constructor, we create an object of type \c EmployeeData and assign it to the \c d pointer using operator=(). Behind the scenes, QSharedDataPointer automatically increments or decrements the reference count of the shared data object pointed to by \c d, and deletes shared objects when the reference count reaches 0. \printline ::Employee(int \printuntil } In the constructor that takes an ID and an employee's name, we also create an object of type \c EmployeeData and assign it to the \c d pointer. \printline ::setName \printuntil /^\}/ When we use the \c d pointer from a non-const function, detach() is automatically called to ensure that we work on our own copy of the data. \printline ::name \printuntil /^\}/ When we use the \c d pointer in a const function, detach() is \e not called. Notice that there is no need to implement a copy constructor or assignment operator in the \c Employee class. This is because the C++ compiler provides default implementations that simply perform member-by-member copy. Here, the only member is \c d, and its operator=() simply increments a reference count (which is precisely what we want). \sa QSharedData */ /*! \fn T &QSharedDataPointer::operator*() Provides access to the shared object's members. This function does a detach(). */ /*! \fn const T &QSharedDataPointer::operator*() const \overload This function does not call detach(). */ /*! \fn T *QSharedDataPointer::operator->() Provides access to the shared object's members. This function does a detach(). */ /*! \fn const T *QSharedDataPointer::operator->() const \overload This function does not call detach(). */ /*! \fn QSharedDataPointer::operator T *() Returns a pointer to the shared object. This function does a detach(). \sa data(), constData() */ /*! \fn QSharedDataPointer::operator const T *() const Returns a pointer to the shared object. This function does not call detach(). */ /*! \fn T * QSharedDataPointer::data() Returns a pointer to the shared object. This function does a detach(). \sa constData() */ /*! \fn const T * QSharedDataPointer::data() const \overload This function does not call detach(). */ /*! \fn const T * QSharedDataPointer::constData() const Returns a const pointer to the shared object. This function does not call detach(). \sa data() */ /*! \fn bool QSharedDataPointer::operator==(const QSharedDataPointer &other) const Returns a true if the pointer to the shared object in \a other is equal to to the pointer to the shared data in this else returns false. This function does not call detach(). */ /*! \fn bool QSharedDataPointer::operator!=(const QSharedDataPointer &other) const Returns a true if the pointer to the shared object in \a other is not equal to to the pointer to the shared data in this else returns false. This function does not call detach(). */ /*! \fn QSharedDataPointer::QSharedDataPointer() Constructs a QSharedDataPointer initialized with a null pointer. */ /*! \fn QSharedDataPointer::~QSharedDataPointer() Destroys the QSharedDataPointer. This function automatically decrements the reference count of the shared object and deletes the object if the reference count reaches 0. */ /*! \fn QSharedDataPointer::QSharedDataPointer(T *sharedData) Constructs a QSharedDataPointer that points to \a sharedData. This function automatically increments \a{sharedData}'s reference count. */ /*! \fn QSharedDataPointer::QSharedDataPointer(const QSharedDataPointer &other) Constructs a copy of \a other. This function automatically increments the reference count of the shared data object pointed to by \a{other}. */ /*! \fn QSharedDataPointer &QSharedDataPointer::operator=(const QSharedDataPointer &other) Assigns \a other to this pointer. This function automatically increments the reference count of the shared data object pointed to by \a{other}, and decrements the reference count of the object previously pointed to by this QSharedDataPointer. If the reference count reaches 0, the shared data object is deleted. */ /*! \fn QSharedDataPointer &QSharedDataPointer::operator=(T *sharedData) \overload Sets this QSharedDataPointer to point to \a sharedData. This function automatically increments \a{sharedData}'s reference count, and decrements the reference count of the object previously pointed to by this QSharedDataPointer. If the reference count reaches 0, the shared data object is deleted. */ /*! \fn bool QSharedDataPointer::operator!() const Returns true if this pointer is null; otherwise returns false. */ /*! \fn void QSharedDataPointer::detach() If the shared data's reference count is greater than 1, creates a deep copy of the shared data. This function is automatically called by QSharedDataPointer when necessary. You should never need to call it yourself. */