Creates a newstd::shared_ptr that shares ownership of the managed object. If there is no managed object, i.e.*this is empty, then the returnedshared_ptr also is empty.

Effectively returnsexpired()? shared_ptr<T>(): shared_ptr<T>(*this), executed atomically.

[edit]Return value

Ashared_ptr which shares ownership of the owned object ifstd::weak_ptr::expired returnsfalse. Else returns default-constructedshared_ptr of typeT.

[edit]Notes

Both this function and the constructor ofstd::shared_ptr may be used to acquire temporary ownership of the managed object referred to by astd::weak_ptr. The difference is that the constructor ofstd::shared_ptr throws an exception when itsstd::weak_ptr argument is empty, whilestd::weak_ptr<T>::lock() constructs an emptystd::shared_ptr<T>.

[edit]Example

#include <iostream>#include <memory> void observe(std::weak_ptr<int> weak){if(auto p= weak.lock())std::cout<<"\tobserve() is able to lock weak_ptr<>, value="<<*p<<'\n';elsestd::cout<<"\tobserve() is unable to lock weak_ptr<>\n";} int main(){std::weak_ptr<int> weak;std::cout<<"weak_ptr<> is not yet initialized\n";    observe(weak); {auto shared=std::make_shared<int>(42);        weak= shared;std::cout<<"weak_ptr<> is initialized with shared_ptr\n";        observe(weak);} std::cout<<"shared_ptr<> has been destructed due to scope exit\n";    observe(weak);}

weak_ptr<> is not yet initialized        observe() is unable to lock weak_ptr<>weak_ptr<> is initialized with shared_ptr        observe() is able to lock weak_ptr<>, value=42shared_ptr<> has been destructed due to scope exit        observe() is unable to lock weak_ptr<>

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

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