# std::enable_shared_from_this<T>::shared_from_this

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< cpp‎ | memory‎ | enable shared from this

std::shared_ptr<T> shared_from_this(); | (1) | (since C++11)
std::shared_ptr<T const> shared_from_this() const; | (2) | (since C++11)

Returns a std::shared_ptr<T> that shares ownership of *this with all existing std::shared_ptr that refer to *this.

Effectively executes std::shared_ptr<T>(weak_this), where `weak-this` is the exposition-only mutable std::weak_ptr<T> member of `enable_shared_from_this`.

### Return value

std::shared_ptr<T> that shares ownership of *this with pre-existing std::shared_ptrs.

### Exceptions

If `shared_from_this` is called on an object that is not previously shared by std::shared_ptr, std::bad_weak_ptr is thrown (by the shared_ptr constructor from a default-constructed `weak-this`).

### Example

Run this code

    #include <iostream>
    #include <memory>

    struct Foo : public std::enable_shared_from_this<Foo>
    {
        Foo() { std::cout << "Foo::Foo\n"; }
        ~Foo() { std::cout << "Foo::~Foo\n"; }
        std::shared_ptr<Foo> getFoo() { return shared_from_this(); }
    };

    int main()
    {
        Foo *f = new Foo;
        std::shared_ptr<Foo> pf1;

        {
            std::shared_ptr<Foo> pf2(f);
            pf1 = pf2->getFoo(); // shares ownership of object with pf2
        }

        std::cout << "pf2 is gone\n";
    }

Output:

    Foo::Foo
    pf2 is gone
    Foo::~Foo

### 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 | calling `shared_from_this` on an unshared object was undefined behavior | std::bad_weak_ptr is thrown

### See also

shared_ptr (C++11) | smart pointer with shared object ownership semantics (class template)

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