std::shared_ptr and this

stackoverflow std::shared_ptr of this

#include <iostream>
#include <memory>
#include <thread>
#include <chrono>
#include <mutex>
#include <list>

class A;
class B;

class A
{
public:
    void addChild(std::shared_ptr<B> child)
    {
        children.push_back(child);

        // How to do pass the pointer correctly?
        // child->setParent(this);  // wrong
        //                  ^^^^
    }

private:
    std::list<std::shared_ptr<B>> children;
};

class B
{
public:
    void setParent(std::shared_ptr<A> parent)
    {
        this->parent = parent;
    }

private:
    std::shared_ptr<A> parent;
};

int main()
{
}
// g++ --std=c++11 test.cpp

The question is how can an object of class A pass a std::shared_ptr of itself (this) to its child?

There are solutions for Boost shared pointers (Getting a boost::shared_ptr for this), but how to handle this using the std:: smart pointers?

A

There is std::enable_shared_from_this just for this purpose. You inherit from it and you can call .shared_from_this() from inside the class. Also, you are creating circular dependencies here that can lead to resource leaks. That can be resolved with the use of std::weak_ptr. So your code might look like this (assuming children rely on existence of parent and not the other way around):

#include <iostream>
#include <memory>
#include <thread>
#include <chrono>
#include <mutex>
#include <list>

class A;
class B;

class A: public std::enable_shared_from_this<A>
{
public:
    void addChild(std::shared_ptr<B> child)
    {
        children.push_back(child);

        // like this
        child->setParent(shared_from_this());  // ok
        //               ^^^^^^^^^^^^^^^^^^
    }

private:
    // note weak_ptr
    std::list<std::weak_ptr<B>> children;
    //             ^^^^^^^^
};

class B
{
public:
    void setParent(std::shared_ptr<A> parent)
    {
        this->parent = parent;
    }

private:
    std::shared_ptr<A> parent;
};

int main()
{
}
// g++ --std=c++11 test.cpp

Note however, that calling .shared_from_this() requires that this is owned by std::shared_ptr at the point of call. This means that you cannot create such object on stack anymore, and generally cannot call .shared_from_this() from within a constructor or destructor.

NOTE: 参见: Requiring-or-Prohibiting-Heap-based-Objects idiom

stackoverflow Getting a boost::shared_ptr for this