Member variable offset

[aquaz]

Hello,
For example, in this class:

class A
{
int a;
int b;
};

Is there any standard way to know the memory offset in bytes between member b of class A and the start of class A(like reinterpret_cast<char*>(this) - reinterpret_cast<char*>(&this->b) but without necessarily instanciate an object A)?
The compiler know it so i see no reason we have to instanciate an object to know it.

[JLBorges]

The offsetof() macro in <cstddef>

[aquaz]

Thank you JLBorges