Defined in header <memory>
template< class T > class enable_shared_from_this;
(since C++11)

std::enable_shared_from_this allows an object t that is currently managed by a std::shared_ptr named pt to safely generate additional std::shared_ptr instances pt1, pt2, ... that all share ownership of t with pt.

Publicly inheriting from std::enable_shared_from_this<T> provides the type T with a member function shared_from_this. If an object t of type T is managed by a std::shared_ptr<T> named pt, then calling T::shared_from_this will return a new std::shared_ptr<T> that shares ownership of t with pt.

Member functions

constructs an enable_shared_from_this object
(protected member function)
destroys an enable_shared_from_this object
(protected member function)
returns a reference to *this
(protected member function)
returns a std::shared_ptr which shares ownership of *this
(public member function)
returns a std::weak_ptr which shares ownership of *this
(public member function)

Member objects

Member name Definition
weak-this (exposition only) std::weak_ptr object tracking the control block of the first shared owner of *this.


A common implementation for enable_shared_from_this is to hold a weak reference (such as std::weak_ptr) to *this. For the purpose of exposition, the weak reference is called weak-this and considered as a mutable std::weak_ptr member.

The constructors of std::shared_ptr detect the presence of an unambiguous and accessible (i.e. public inheritance is mandatory) enable_shared_from_this base and assign the newly created std::shared_ptr to weak-this if not already owned by a live std::shared_ptr. Constructing a std::shared_ptr for an object that is already managed by another std::shared_ptr will not consult weak-this and thus will lead to undefined behavior.

It is permitted to call shared_from_this only on a previously shared object, i.e. on an object managed by std::shared_ptr<T>. Otherwise, std::bad_weak_ptr is thrown (by the shared_ptr constructor from a default-constructed weak-this).

enable_shared_from_this provides the safe alternative to an expression like std::shared_ptr<T>(this), which is likely to result in this being destructed more than once by multiple owners that are unaware of each other (see example below).


#include <iostream>
#include <memory>
class Good : public std::enable_shared_from_this<Good>
    std::shared_ptr<Good> getptr()
        return shared_from_this();
class Best : public std::enable_shared_from_this<Best>
    std::shared_ptr<Best> getptr()
        return shared_from_this();
    // No public constructor, only a factory function,
    // so there's no way to have getptr return nullptr.
    [[nodiscard]] static std::shared_ptr<Best> create()
        // Not using std::make_shared<Best> because the c'tor is private.
        return std::shared_ptr<Best>(new Best());
    Best() = default;
struct Bad
    std::shared_ptr<Bad> getptr()
        return std::shared_ptr<Bad>(this);
    ~Bad() { std::cout << "Bad::~Bad() called\n"; }
void testGood()
    // Good: the two shared_ptr's share the same object
    std::shared_ptr<Good> good0 = std::make_shared<Good>();
    std::shared_ptr<Good> good1 = good0->getptr();
    std::cout << "good1.use_count() = " << good1.use_count() << '\n';
void misuseGood()
    // Bad: shared_from_this is called without having std::shared_ptr owning the caller
        Good not_so_good;
        std::shared_ptr<Good> gp1 = not_so_good.getptr();
    catch (std::bad_weak_ptr& e)
        // undefined behavior (until C++17) and std::bad_weak_ptr thrown (since C++17)
        std::cout << e.what() << '\n';
void testBest()
    // Best: Same but can't stack-allocate it:
    std::shared_ptr<Best> best0 = Best::create();
    std::shared_ptr<Best> best1 = best0->getptr();
    std::cout << "best1.use_count() = " << best1.use_count() << '\n';
    // Best stackBest; // <- Will not compile because Best::Best() is private.
void testBad()
    // Bad, each shared_ptr thinks it's the only owner of the object
    std::shared_ptr<Bad> bad0 = std::make_shared<Bad>();
    std::shared_ptr<Bad> bad1 = bad0->getptr();
    std::cout << "bad1.use_count() = " << bad1.use_count() << '\n';
} // UB: double-delete of Bad
int main()

Possible output:

good1.use_count() = 2
best1.use_count() = 2
bad1.use_count() = 1
Bad::~Bad() called
Bad::~Bad() called
*** glibc detected *** ./test: double free or corruption

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 2529 C++11 specification for enable_shared_from_this was unclear and maybe unimplementable clarified and fixed

See also

smart pointer with shared object ownership semantics
(class template)
creates a shared pointer that manages a new object
(function template)

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