23 General utilities library [utilities]

23.11 Smart pointers [smartptr]

23.11.2 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.

bool expired() const noexcept;

Returns: use_­count() == 0.

shared_ptr<T> lock() const noexcept;

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

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