20 General utilities library [utilities]

20.7 Smart pointers [smartptr]

20.7.2 Shared-ownership pointers [util.smartptr]

20.7.2.2 Class template shared_ptr [util.smartptr.shared]

20.7.2.2.9 shared_ptr casts [util.smartptr.shared.cast]

template<class T, class U> shared_ptr<T> static_pointer_cast(const shared_ptr<U>& r) noexcept;

1

Requires: The expression static_cast<T*>(r.get()) shall be well formed.

2

Returns: If r is empty, an empty shared_ptr<T>; otherwise, a shared_ptr<T> object that stores static_cast<T*>(r.get()) and shares ownership with r.

3

Postconditions: w.get() == static_cast<T*>(r.get()) and w.use_count() == r.use_count(), where w is the return value.

4

[ Note: The seemingly equivalent expression shared_ptr<T>(static_cast<T*>(r.get())) will eventually result in undefined behavior, attempting to delete the same object twice.  — end note ]

template<class T, class U> shared_ptr<T> dynamic_pointer_cast(const shared_ptr<U>& r) noexcept;

5

Requires: The expression dynamic_cast<T*>(r.get()) shall be well formed and shall have well defined behavior.

6

Returns:

  • (6.1)

    When dynamic_cast<T*>(r.get()) returns a nonzero value, a shared_ptr<T> object that stores a copy of it and shares ownership with r;

  • (6.2)

    Otherwise, an empty shared_ptr<T> object.

7

Postcondition: w.get() == dynamic_cast<T*>(r.get()), where w is the return value.

8

[ Note: The seemingly equivalent expression shared_ptr<T>(dynamic_cast<T*>(r.get())) will eventually result in undefined behavior, attempting to delete the same object twice.  — end note ]

template<class T, class U> shared_ptr<T> const_pointer_cast(const shared_ptr<U>& r) noexcept;

9

Requires: The expression const_cast<T*>(r.get()) shall be well formed.

10

Returns: If r is empty, an empty shared_ptr<T>; otherwise, a shared_ptr<T> object that stores const_cast<T*>(r.get()) and shares ownership with r.

11

Postconditions: w.get() == const_cast<T*>(r.get()) and w.use_count() == r.use_count(), where w is the return value.

12

[ Note: The seemingly equivalent expression shared_ptr<T>(const_cast<T*>(r.get())) will eventually result in undefined behavior, attempting to delete the same object twice.  — end note ]