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";
}
Foo::Foo
pf2 is gone
Foo::~Foo