c - size of a datatype without using sizeof

Question

I have a data type, say X, and I want to know its size without declaring a variable or pointer of that type and of course without using sizeof operator.

Is this possible? I thought of using standard header files which contain size and range of data types but that doesn't work with user defined data type.

Answer 1

To my mind, this fits into the category of "how do I add two ints without using ++, += or + ?". It's a waste of time. You can try and avoid the monsters of undefined behaviour by doing something like this.

size_t size = (size_t)(1 + ((X*)0));

Note that I don't declare a variable of type or pointer to X.