It depends. Clang, GCC and the Intel C++ compiler all support #pragma once perfectly. Personally, I prefer it, as it is only one line rather than three and I do

It depends. Clang, GCC and the Intel C++ compiler all support #pragma once perfectly. Personally, I prefer it, as it is only one line rather than three and I don’t have to think of a unique name for the header guard. Supposedly it breaks if you play weird tricks with the filesystem (s.t. the compiler thinks two identical files are actually different), but I have never encountered such breakage.