std::enable_shared_from_this<T>::shared_from_this

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std::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

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