/qt-everywhere-opensource-src-4.8.2/src/corelib/tools/qscopedpointer.cpp
C++ | 282 lines | 3 code | 23 blank | 256 comment | 0 complexity | c0dc817459d307e080241f7490103ec1 MD5 | raw file
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- #include "qscopedpointer.h"
- QT_BEGIN_NAMESPACE
- /*!
- \class QScopedPointer
- \brief The QScopedPointer class stores a pointer to a dynamically allocated object, and deletes it upon destruction.
- \since 4.6
- \reentrant
- \ingroup misc
- Managing heap allocated objects manually is hard and error prone, with the
- common result that code leaks memory and is hard to maintain.
- QScopedPointer is a small utility class that heavily simplifies this by
- assigning stack-based memory ownership to heap allocations, more generally
- called resource acquisition is initialization(RAII).
- QScopedPointer guarantees that the object pointed to will get deleted when
- the current scope disappears.
- Consider this function which does heap allocations, and have various exit points:
- \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 0
- It's encumbered by the manual delete calls. With QScopedPointer, the code
- can be simplified to:
- \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 1
- The code the compiler generates for QScopedPointer is the same as when
- writing it manually. Code that makes use of \a delete are candidates for
- QScopedPointer usage (and if not, possibly another type of smart pointer
- such as QSharedPointer). QScopedPointer intentionally has no copy
- constructor or assignment operator, such that ownership and lifetime is
- clearly communicated.
- The const qualification on a regular C++ pointer can also be expressed with
- a QScopedPointer:
- \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 2
- \section1 Custom cleanup handlers
- Arrays as well as pointers that have been allocated with \c malloc must
- not be deleted using \c delete. QScopedPointer's second template parameter
- can be used for custom cleanup handlers.
- The following custom cleanup handlers exist:
- \list
- \i QScopedPointerDeleter - the default, deletes the pointer using \c delete
- \i QScopedPointerArrayDeleter - deletes the pointer using \c{delete []}. Use
- this handler for pointers that were allocated with \c{new []}.
- \i QScopedPointerPodDeleter - deletes the pointer using \c{free()}. Use this
- handler for pointers that were allocated with \c{malloc()}.
- \endlist
- You can pass your own classes as handlers, provided that they have a public
- static function \c{void cleanup(T *pointer)}.
- \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 5
- \section1 Forward Declared Pointers
- Classes that are forward declared can be used within QScopedPointer, as
- long as the destructor of the forward declared class is available whenever
- a QScopedPointer needs to clean up.
- Concretely, this means that all classes containing a QScopedPointer that
- points to a forward declared class must have non-inline constructors,
- destructors and assignment operators:
- \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 4
- Otherwise, the compiler output a warning about not being able to destruct
- \c MyPrivateClass.
- \sa QSharedPointer
- */
- /*! \typedef QScopedPointer::pointer
- \internal
- */
- /*!
- \fn QScopedPointer::QScopedPointer(T *p = 0)
- Constructs this QScopedPointer instance and sets its pointer to \a p.
- */
- /*!
- \fn QScopedPointer::~QScopedPointer()
- Destroys this QScopedPointer object. Delete the object its pointer points
- to.
- */
- /*!
- \fn T *QScopedPointer::data() const
- Returns the value of the pointer referenced by this object. QScopedPointer
- still owns the object pointed to.
- */
- /*!
- \fn T &QScopedPointer::operator*() const
- Provides access to the scoped pointer's object.
- If the contained pointer is \c null, behavior is undefined.
- \sa isNull()
- */
- /*!
- \fn T *QScopedPointer::operator->() const
- Provides access to the scoped pointer's object.
- If the contained pointer is \c null, behavior is undefined.
- \sa isNull()
- */
- /*!
- \fn QScopedPointer::operator bool() const
- Returns \c true if this object is not \c null. This function is suitable
- for use in \tt if-constructs, like:
- \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 3
- \sa isNull()
- */
- /*!
- \fn bool operator==(const QScopedPointer<T, Cleanup> &lhs, const QScopedPointer<T, Cleanup> &rhs)
- Equality operator. Returns true if the scoped pointers
- \a lhs and \a rhs are pointing to the same object.
- Otherwise returns false.
- */
- /*!
- \fn bool operator!=(const QScopedPointer<T, Cleanup> &lhs, const QScopedPointer<T, Cleanup> &rhs)
- Inequality operator. Returns true if the scoped pointers
- \a lhs and \a rhs are \e not pointing to the same object.
- Otherwise returns false.
- */
- /*!
- \fn bool QScopedPointer::isNull() const
- Returns \c true if this object is holding a pointer that is \c null.
- */
- /*!
- \fn void QScopedPointer::reset(T *other = 0)
- Deletes the existing object it is pointing to if any, and sets its pointer to
- \a other. QScopedPointer now owns \a other and will delete it in its
- destructor.
- */
- /*!
- \fn T *QScopedPointer::take()
- Returns the value of the pointer referenced by this object. The pointer of this
- QScopedPointer object will be reset to \c null.
- Callers of this function take ownership of the pointer.
- */
- /*! \fn bool QScopedPointer::operator!() const
- Returns \c true if the pointer referenced by this object is \c null, otherwise
- returns \c false.
- \sa isNull()
- */
- /*! \fn void QScopedPointer::swap(QScopedPointer<T, Cleanup> &other)
- Swap this pointer with \a other.
- */
- /*!
- \class QScopedArrayPointer
- \brief The QScopedArrayPointer class stores a pointer to a
- dynamically allocated array of objects, and deletes it upon
- destruction.
- \since 4.6
- \reentrant
- \ingroup misc
- A QScopedArrayPointer is a QScopedPointer that defaults to
- deleting the object it is pointing to with the delete[] operator. It
- also features operator[] for convenience, so we can write:
- \code
- void foo()
- {
- QScopedArrayPointer<int> i(new int[10]);
- i[2] = 42;
- ...
- return; // our integer array is now deleted using delete[]
- }
- \endcode
- */
- /*!
- \fn QScopedArrayPointer::QScopedArrayPointer()
- Constructs a QScopedArrayPointer instance.
- */
- /*!
- \fn T *QScopedArrayPointer::operator[](int i)
- Provides access to entry \a i of the scoped pointer's array of
- objects.
- If the contained pointer is \c null, behavior is undefined.
- \sa isNull()
- */
- /*!
- \fn T *QScopedArrayPointer::operator[](int i) const
- Provides access to entry \a i of the scoped pointer's array of
- objects.
- If the contained pointer is \c null, behavior is undefined.
- \sa isNull()
- */
- QT_END_NAMESPACE