How can you find the size of a datatype without creating a variable or pointer, or using sizeof of the datatype?

Question

The question shown below is an interview question:

Q) You are given/have a datatype, say X in C.

The requirement is to get the size of the datatype, without decl

Answer 1

define sizeof_type( type ) (size_t)((type*)1000 + 1 )-(size_t)((type*)1000)

The original is from this discussion. http://www.linuxquestions.org/questions/programming-9/how-to-know-the-size-of-the-variable-without-using-sizeof-469920/