Is #pragma once a safe include guard?

Question

I\'ve read that there is some compiler optimization when using #pragma once which can result in faster compilation. I recognize that is non-standard, and thus

Answer 1

#pragma once does have one drawback (other than being non-standard) and that is if you have the same file in different locations (we have this because our build system copies files around) then the compiler will think these are different files.