The QExplicitlySharedDataPointer class represents a pointer to an explicitly shared object. 更多...
| 头： | #include <QExplicitlySharedDataPointer> |
| qmake: | QT += core |
| Since: | Qt 4.4 |
该类在 Qt 4.4 引入。
注意： 此类的所有函数 可重入 .
| typedef | Type |
| QExplicitlySharedDataPointer (QExplicitlySharedDataPointer<T> && o ) | |
| QExplicitlySharedDataPointer (const QExplicitlySharedDataPointer<X> & o ) | |
| QExplicitlySharedDataPointer (const QExplicitlySharedDataPointer<T> & o ) | |
| QExplicitlySharedDataPointer (T * data ) | |
| QExplicitlySharedDataPointer () | |
| QExplicitlySharedDataPointer<T> & | operator= (QExplicitlySharedDataPointer<T> && other ) |
| QExplicitlySharedDataPointer<T> & | operator= (const QExplicitlySharedDataPointer<T> & o ) |
| ~QExplicitlySharedDataPointer () | |
| const T * | constData () const |
| T * | data () const |
| void | detach () |
| void | reset () |
| void | swap (QExplicitlySharedDataPointer<T> & other ) |
| T * | take () |
| bool | operator bool () const |
| bool | operator! () const |
| bool | operator!= (const QExplicitlySharedDataPointer<T> & other ) const |
| bool | operator!= (const T * ptr ) const |
| T & | operator* () const |
| T * | operator-> () |
| T * | operator-> () const |
| QExplicitlySharedDataPointer<T> & | operator= (T * o ) |
| bool | operator== (const QExplicitlySharedDataPointer<T> & other ) const |
| bool | operator== (const T * ptr ) const |
| T * | clone () |
QExplicitlySharedDataPointer<T> makes writing your own explicitly shared classes easy. QExplicitlySharedDataPointer implements thread-safe reference counting, ensuring that adding QExplicitlySharedDataPointers to your 可重入 classes won't make them non-reentrant.
Except for one big difference, QExplicitlySharedDataPointer is just like QSharedDataPointer . The big difference is that member functions of QExplicitlySharedDataPointer do not do the automatic copy on write operation ( detach ()) that non-const members of QSharedDataPointer do before allowing the shared data object to be modified. There is a detach () function available, but if you really want to detach (), you have to call it yourself. This means that QExplicitlySharedDataPointers behave like regular C++ pointers, except that by doing reference counting and not deleting the shared data object until the reference count is 0, they avoid the dangling pointer problem.
It is instructive to compare QExplicitlySharedDataPointer with QSharedDataPointer by way of an example. Consider the Employee example in QSharedDataPointer , modified to use explicit sharing as explained in the discussion 隐式 vs 明确共享 .
Note that if you use this class but find you are calling detach () a lot, you probably should be using QSharedDataPointer 代替。
In the member function documentation, d pointer always refers to the internal pointer to the shared data object.
另请参阅 QSharedData and QSharedDataPointer .
这是共享数据对象的类型。 d pointer 指向此类型的对象。
Move-constructs a QExplicitlySharedDataPointer instance, making it point at the same object that o 所指向的。
该函数在 Qt 5.2 引入。
This copy constructor is different in that it allows o to be a different type of explicitly shared data pointer but one that has a compatible shared data object.
默认情况下，
d pointer
of
o
(of type
X *
) gets implicitly converted to the type
T *
; the result of this conversion is set as the
d pointer
of
this
, and the reference count of the shared data object is incremented.
However, if the macro
QT_ENABLE_QEXPLICITLYSHAREDDATAPOINTER_STATICCAST
is defined before including the
QExplicitlySharedDataPointer
header, then the
d pointer
of
o
undergoes a
static_cast
to the type
T *
. The result of the cast is then set as the
d pointer
of
this
, and the reference count of the shared data object is incremented.
警告：
relying on such
static_cast
is potentially dangerous, because it allows code like this to compile:
QExplicitlySharedDataPointer<Base> base(new Base);
QExplicitlySharedDataPointer<Derived> derived(base); // !!! DANGER !!!
Starting from Qt 5.4 the cast is disabled by default. It is possible to enable it back by defining the
QT_ENABLE_QEXPLICITLYSHAREDDATAPOINTER_STATICCAST
macro, and therefore to allow old code (that relied on this feature) to compile without modifications.
This standard copy constructor sets the d pointer of this 到 d pointer in o and increments the reference count of the shared data object.
Constructs a QExplicitlySharedDataPointer with d pointer 设为 data 并递增 data 的引用计数。
Constructs a QExplicitlySharedDataPointer initialized with
nullptr
as
d pointer
.
移动赋值 other 到此 QExplicitlySharedDataPointer 实例。
该函数在 Qt 5.2 引入。
设置 d pointer of this 到 d pointer of o and increments the reference count of the shared data object. The reference count of the old shared data object of this is decremented. If the reference count of the old shared data object becomes 0, the old shared data object is deleted.
Decrements the reference count of the shared data object. If the reference count becomes 0, the shared data object is deleted. This is then destroyed.
[protected]
T
*QExplicitlySharedDataPointer::
clone
()
Creates and returns a deep copy of the current data. This function is called by detach () when the reference count is greater than 1 in order to create the new copy. This function uses the operator new and calls the copy constructor of the type T.
见 QSharedDataPointer <T>::clone() for an explanation of how to use it.
该函数在 Qt 4.5 引入。
返回共享数据对象的 const 指针。
另请参阅 data ().
返回共享数据对象指针。
If the shared data object's reference count is greater than 1, this function creates a deep copy of the shared data object and sets the d pointer of this to the copy.
因为 QExplicitlySharedDataPointer does not do the automatic copy on write operations that members of QSharedDataPointer do, detach() is not called automatically anywhere in the member functions of this class. If you find that you are calling detach() everywhere in your code, consider using QSharedDataPointer 代替。
重置
this
to be null - i.e., this function sets the
d pointer
of
this
to
nullptr
, but first it decrements the reference count of the shared data object and deletes the shared data object if the reference count became 0.
Swap this instance's explicitly shared data pointer with the explicitly shared data pointer in other .
Returns a pointer to the shared object, and resets
this
到
nullptr
. (That is, this function sets the
d pointer
of
this
to
nullptr
)。
注意： The reference count of the returned object will not be decremented.
该函数在 Qt 5.12 引入。
返回
true
若
d pointer
of
this
is
not
null.
返回
true
若
d pointer
of
this
is
nullptr
.
返回
true
if
other
and
this
do
not
有相同
d pointer
.
返回
true
若
d pointer
of
this
is
not
ptr
.
Provides access to the shared data object's members.
Provides access to the shared data object's members.
Provides const access to the shared data object's members.
设置 d pointer of this to o 并递增 o 's reference count. The reference count of the old shared data object of this is decremented. If the reference count of the old shared data object becomes 0, the old shared data object is deleted.
返回
true
if
other
and
this
有相同
d pointer
.
返回
true
若
d pointer
of
this
is
ptr
.