Ryan Emerle Ryan Emerle -4 years ago 45
C++ Question

Is #pragma once a safe include guard?

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 could pose a cross-platform compatibility issue.

Is this something that is supported by most modern compilers on non-windows platforms (gcc)?

I want to avoid platform compilation issues, but also want to avoid the extra work of fallback guards:

#pragma once
#ifndef HEADER_H
#define HEADER_H

...

#endif // HEADER_H


Should I be concerned? Should I expend any further mental energy on this?

Answer Source

It should work on any modern compiler, but I don't see any reason not to use a standard #ifndef include guard. It works just fine. The one caveat is that GCC didn't support it before version 3.4.

I also found that, at least on GCC, it recognizes the standard #ifndef include guard and optimizes it, so it shouldn't be much slower than #pragma once.

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