20 General utilities library [utilities]

20.11 Smart pointers [smartptr]

20.11.4 Class template weak_­ptr [util.smartptr.weak] 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 noexcept; template<class U> bool owner_before(const weak_ptr<U>& b) const noexcept;
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.