How does sizeof work? How can I write my own?

Question

I know C++ and know the function sizeof itself but I need to write my own sizeof function so please explain how it works exactly? What does it do with the parameter

Answer 1

sizeof is an C++ operator which yields the number of bytes in the object representation of its operand. Result of sizeof is an implementation-defined constant of type size_t, but should meet the requirements set forth in C++ Standard 5.3.3. You could write your own type traits that will work similar to built-in sizeof operator.

template struct get_sizeof;

template<> struct get_sizeof          { static const size_t value = 1; };
template<> struct get_sizeof { static const size_t value = 1; };
template<> struct get_sizeof           { static const size_t value = 4; };
template<> struct get_sizeof          { static const size_t value = 4; };
// etc.

...
// sample of use
static const size_t size = get_sizeof::value;
char x[get_sizeof::value];

But this have no sense since only creators of the compiler are knows actual values of value for the implementation.