See http://timepit.eu/~frank/blog/2013/03/enable_weak_from_this/ for more information.

enable_weak_from_this.h

#include <memory>

template<class T>
struct enable_weak_from_this {
  enable_weak_from_this() : ref_{static_cast<T*>(this), nopDeleter} {}

  std::weak_ptr<T> weak_from_this() const {
    return ref_;
  }

 private:
  static void nopDeleter(void*) {}

  std::shared_ptr<T> ref_;
};

test.cpp

#include <iostream>
#include "enable_weak_from_this.h"

struct B;

struct A : enable_weak_from_this<A> {
  void hello() const { std::cout << "A::hello called\n"; }

  B* createB() const;
};

struct B {
  B(const std::weak_ptr<A>& creator) : creator_{creator} {}

  void callHello() const {
    if (auto a = creator_.lock()) {
      a->hello();
    } else {
      std::cout << "creator_ has been destroyed\n";
    }
  }

 private:
  std::weak_ptr<A> creator_;
};

B* A::createB() const { 
  return new B{weak_from_this()};
}


int main(int argc, char* argv[]) {
  auto a = new A;
  auto b = a->createB();
  
  b->callHello();
  delete a;
  b->callHello();
  delete b;
}

// $ g++ -std=c++11 test.cpp
// $ ./a.out
// A::hello called
// creator_ has been destroyed