C++, is it possible to call a constructor directly, without new?

Question

Can I call constructor explicitly, without using new, if I already have a memory for object?

class Object1{
    char *str;
public:
    Object1(c         


        

Answer 1

You can use the following template

template <typename T, typename... Args>
inline void InitClass(T &t, Args... args)
{
    t.~T();
    new (&t) T(args...);
}

usage:

struct A
{
   A() {}
   A(int i) : a(i) {}
   int a;
} my_value;

InitClass(my_value);
InitClass(my_value, 5);

Answer 2

Yes, when you've got your own allocated buffer you use placement new. Brian Bondy has a good response here in a related question:

What uses are there for "placement new"?

Answer 3

I think you're looking for Placement New. The C++ FAQ Lite has a good summary of how you do this. There are a few important gotchas from this entry:

1. You're supposed to #include <new> to use the placement new syntax.
2. Your memory buffer needs to be properly aligned for the object you are creating.
3. It's your job to manually call the destructor.