[util.smartptr.shared.obs]

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constexpr element_type* get() const noexcept;

Returns: The stored pointer.

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constexpr T& operator*() const noexcept;

Remarks: When T is an array type or cv void, it is unspecified whether this member function is declared.

If it is declared, it is unspecified what its return type is, except that the declaration (although not necessarily the definition) of the function shall be well-formed.

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constexpr T* operator->() const noexcept;

Remarks: When T is an array type, it is unspecified whether this member function is declared.

If it is declared, it is unspecified what its return type is, except that the declaration (although not necessarily the definition) of the function shall be well-formed.

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constexpr element_type& operator[](ptrdiff_t i) const;

Throws: Nothing.

Remarks: When T is not an array type, it is unspecified whether this member function is declared.

If it is declared, it is unspecified what its return type is, except that the declaration (although not necessarily the definition) of the function shall be well-formed.

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constexpr long use_count() const noexcept;

Returns: The number of shared_ptr objects, *this included, that share ownership with *this, or 0 when *this is empty.

[Note 1:

get() == nullptr does not imply a specific return value of use_count().

— end note]

[Note 2:

weak_ptr<T>::lock() can affect the return value of use_count().

— end note]

[Note 3:

When multiple threads might affect the return value of use_count(), the result is approximate.

In particular, use_count() == 1 does not imply that accesses through a previously destroyed shared_ptr have in any sense completed.

— end note]

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constexpr explicit operator bool() const noexcept;

Returns: get() != nullptr.

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template<class U> constexpr bool owner_before(const shared_ptr<U>& b) const noexcept;
template<class U> constexpr bool owner_before(const weak_ptr<U>& b) const noexcept;

Returns: An unspecified value such that

(19.1)
owner_before(b) defines a strict weak ordering as defined in [alg.sorting];
(19.2)
!owner_before(b) && !b.owner_before(*this) is true if and only if owner_equal(b) is true.

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size_t owner_hash() const noexcept;

Returns: An unspecified value such that, for any object x where owner_equal(x) is true, owner_hash() == x.owner_hash() is true.

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template<class U>
  constexpr bool owner_equal(const shared_ptr<U>& b) const noexcept;
template<class U>
  constexpr bool owner_equal(const weak_ptr<U>& b) const noexcept;

Returns: true if and only if *this and b share ownership or are both empty.

Otherwise returns false.

Remarks: owner_equal is an equivalence relation.

20 Memory management library [mem]

20.3 Smart pointers [smartptr]

20.3.2 Shared-ownership pointers [util.sharedptr]

20.3.2.2 Class template shared_ptr [util.smartptr.shared]

20.3.2.2.6 Observers [util.smartptr.shared.obs]