NAME¶

std::enable_shared_from_this::shared_from_this - std::enable_shared_from_this::shared_from_this

Synopsis¶

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
calling shared_from_this on an
LWG 2529 C++11 unshared object was undefined std::bad_weak_ptr is thrown
behavior

See also¶

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