20 General utilities library [utilities]

20.8 Smart pointers [smartptr]

20.8.2 Shared-ownership pointers [util.smartptr] Class template weak_ptr [util.smartptr.weak] weak_ptr observers [util.smartptr.weak.obs]

long use_count() const noexcept;

Returns: 0 if *this is empty; otherwise, the number of shared_ptr instances that share ownership with *this.

Note: use_count() is not necessarily efficient. — end note ]

bool expired() const noexcept;

Returns: use_count() == 0.

Note: expired() may be faster than use_count().  — end note ]

shared_ptr<T> lock() const noexcept;

Returns: expired() ? shared_ptr<T>() : shared_ptr<T>(*this), executed atomically.

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

Returns: An unspecified value such that

  • x.owner_before(y) defines a strict weak ordering as defined in [alg.sorting];

  • under the equivalence relation defined by owner_before, !a.owner_before(b) && !b.owner_before(a), two shared_ptr or weak_ptr instances are equivalent if and only if they share ownership or are both empty.