Question: In trying to learn how to use std::aligned\_union I am having trouble finding any examples. My attempt is running into problems that I do not know how to solve.

```
struct include
{
    std::string file;
};
struct use
{
    use(const std::string &from, const std::string &to) : from{ from }, to{ to }
    {
    }
    std::string from;
    std::string to;
};
std::aligned_union<sizeof(use), include, use>::type item;
*reinterpret_cast<use*>(&item_) = use{ from, to };

```

When I attempt to run the program in VC++2013 debug mode I get a runtime error in `memcpy(unsigned char * dst, unsigned char * src, unsigned long count)`. I assume that this is how VC++ implements the assignment from the temporary.

How would I change this so that I do not have this issue?

Answer: 
The `aligned_union` type gives you a POD type that's suitable as storage for the desired classes - it is not actually an *object* of that type. You still have to construct your own object:

```
#include <memory>

{
    std::aligned_union<sizeof(use), include, use>::type storage;

    use * p = new (static_cast<void*>(std::addressof(storage))) use(from, to);

    // ...

    p->~use();
}

```
Expanding on [Kerrek's answer](https://stackoverflow.com/a/21568809/923854): I suggest using `unique_ptr` with custom deleter to handle the destruction for you automatically. You can wrap everything up nicely in a factory ([Live at Rextester](http://rextester.com/PSXH66839)):

```
struct placement_deleter {
  template <typename T>
  void operator () (T* ptr) const {
    ptr->~T();
  }
};

template <typename T, typename...Args>
std::unique_ptr<T, placement_deleter>
make_in_place(void* place, Args&&...args) {
  return std::unique_ptr<T, placement_deleter>{
    ::new (place) T(std::forward<Args>(args)...)
  };
}

int main() {
  std::aligned_union<0, int, std::string>::type storage;
  {
    auto i = make_in_place<int>(&storage, 42);
    std::cout << *i << '\n';
  }
  {
    auto s = make_in_place<std::string>(&storage, "this is");
    *s += " a test";
    std::cout << *s << '\n';
  }
}

```