(8) of http://en.cppreference.com/w/cpp/memory/shared_ptr/shared_ptr

aliasing_constructor.cpp

#include <iostream>
#include <memory>

std::shared_ptr<int*> CreatePointerNG(int v) {
  auto foo = std::make_shared<int>(v);
  return std::make_shared<int*>(foo.get());
}

std::shared_ptr<int*> CreatePointerOK(int v) {
  auto foo = std::make_shared<int>(v);
  std::shared_ptr<int*> p(foo, new int*(foo.get()));
  return p;
}

int main() {
  auto p1 = CreatePointerNG(100);
  std::cout << "p1: " << *p1 << " " << **p1 << std::endl;

  auto p2 = CreatePointerOK(200);
  std::cout << "p2: " << *p2 << " " << **p2 << std::endl; // p1 is deleted
  std::cout << "p1: " << *p1 << " " << **p1 << std::endl; // then reused

  auto p3 = CreatePointerOK(300);
  std::cout << "p3: " << *p3 << " " << **p3 << std::endl; // p2 is alive
  std::cout << "p2: " << *p2 << " " << **p2 << std::endl; // then not reused.
  return 0;
}

// p1: 0x7fdf20d00018 100
// p2: 0x7fdf20d00018 200
// p1: 0x7fdf20d00018 200
// p3: 0x7fdf20d00068 300
// p2: 0x7fdf20d00018 200