C - Find the size of structure

Question

I was asked this as interview question. Couldn\'t answer.

Write a C program to find size of structure without using the sizeof operator.

Answer 1

Here's two macro versions for the two forms of sizeof (takes a type vs. takes a variable) that you can use for all the code you'll never write where you aren't allowed to use sizeof:

#define type_sizeof(t) (size_t)((char *)((t *)1024 + 1) - (char *)((t *)1024))
#define var_sizeof(v)  (size_t)((char *)(&(v) + 1) - (char *)&(v))

Perhaps with some deep magic you can combine the two into a single macro that will almost serve as a drop-in replacement in all this sizeof-less code. (Too bad you can't fix the multiple-evaluation bugs.)