c++ - Why doesn't sizeof parse struct members? -

I know that sizeof is a compile time calculation, but it seems strange to me: The compiler can either take a type of name, or an expression (on which it reduces the type). But how do you identify one type within a class? This is the only way to pass an expression, which seems very clunky.

  struct x {int x; }; Int main () {// Return size (X :: X); // Return size does not work (x ::) :: x); // works, and X needs to be default-able)  

An alternative method works without the need for a default constructor:

  return size ((x *) 0) -> gt; x);  

You can wrap it in a macro, so that it can be read better:

  #define member_sizeof (T, F) sizeof (( * T *) 0) - & gt; F)