Question

please can anybody help me to implement sizeof() operator in c..

i know the usage .. but i was not able to implement it.

Answer 1

You can’t implement sizeof in C; it’s a basic operator (you can’t implement + either).

You could write a macro that has a limited subset of sizeof‘s behavior, by doing something along the lines of:

#define thisIsAHorribleHackDontDoThis(a) \
    ((size_t)((intptr_t)(&a + 1) - (intptr_t)&a))

but that only works if a is an lvalue (and it’s horrible to behold). sizeof is not so limited, and that’s why you should use it instead of reinventing a wheel that isn’t actually round.