create std::string from char* in a safe way

string foo()
{
  char *p = get_string();

  string str( p );
  free( p );
  return str;
}

string
foo()
{
    shared_ptr<char> p(get_string(), &free);
    string str(p.get());
    return str;
}

string foo()
{
    const char* p = get_string();
    const Cleanup cleanup(p);
    const std::string str(p != NULL ? p : "");

    return str;
}

struct Cleanup {
        void* toFree;
        Cleanup(void* toFree) : toFree(toFree) {}
        ~Cleanup() { free(toFree); }
    private:
        Cleanup(Cleanup&);
        void operator=(Cleanup&);
};

string foo()
{
  char *p = get_string();
  ScopeGuard sg = MakeGuard(&free, p);
  string str( p );
  return str;
}