Re: detecting class member offset from member itself
Frederick Gotham wrote:
(char*)&GetObj< type >(). member - (char*)&GetObj< type >()
Another undefined behavior, isn't it?
According to 5.7, we have pointer addition/subtraction operation
defined, and unfortunately, your above MACRO will invoke
undefined behavior (5.7/p6).
No it won't invoke undefined behaviour. Firstly, any pointer address can
stored in a char*.
Are you talking about PODs?
Secondly, if two pointers point to parts of the same
object, then they can be subracted to give a distance.
Please read 5.7 again. The subtraction operation works for object
itself and you can not apply it to the object's members.
The Standard necessitates that the code work perfectly.
I do not see how it works perfectly. There are many ways to
break it in my mind.
int i = 1;
const int foo::a;
// static member OK?
static const int a = 2;
// reference member OK?
const int &b;
// overloaded operator OK?
// inaccessible default constructor OK?
If you apply your Macro to this class/members, you will find
strange results in my mind.
To repeat myself, offsetof (or Macros like it) is seldom useful
in our c++ context. Avoid them if possible please.
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