[boost] How to create a shallow copy without calling a constructor?

Subject: [boost] How to create a shallow copy without calling a constructor?
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2010-01-02 10:42:45

Hello,

While developing Boost.STM (Software Transactional Memory), I need to create a cache of a transactional object without using the new operator nor the copy constructor of the class. This cache needs only to copy the raw memory of the copied instance, is for that I have called it shallow_clone

The following will create a deep copy and don't respect my requirements

class C {
public:
  C* shallow_clone() {
      return new C(*this);
  }
};

I have looked at uninitialized_copy but if I have understood it correctly, it calls the copy constructor. 
I have tried with

class C {
public:
  C* shallow_clone() {
     C* p = reinterpret_cast<C>(malloc(sizeof(C));
      if (p==0) {
          throw std::bad_alloc();
      }
      memcpy(p, this, sizeof(C));
      return p;
  }
};

But I suspect that this is not correct in general. Is this correct on some particular cases? if yes on witch ones?
Is there a way to create such a cache instance without calling to the constructor in a portable way using some low level C++ interface? 

Thanks,
Vicente

_____________________
Vicente Juan Botet Escribá