std::enable_shared_from_this<T>::shared_from_this

std::shared_ptr<T> shared_from_this();              (1)
std::shared_ptr<T const> shared_from_this() const;  (2)

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 private mutable std::weak_ptr<T> member of enable_shared_from_this.

Notes

It is permitted to call shared_from_this only on a previously shared object, i.e. on an object managed by std::shared_ptr (in particular, shared_from_this cannot be called during construction of *this).

Otherwise the behavior is undefined (until C++17) / std::bad_weak_ptr is thrown (by the shared_ptr constructor from a default-constructed weak_this) (since C++17).

Return value

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

Example

Note: enable_shared_from_this::operator= is defined as protected in order to prevent accidental slicing but allow derived classes to have default assignment operators.

#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";   
}

Result

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