#pragma 曾经是一个安全的包含守卫吗? [英] Is #pragma once a safe include guard?

问题描述

我读到在使用 #pragma once 时有一些编译器优化，这可以导致更快的编译.我承认这是非标准的，因此可能会造成跨平台兼容性问题.

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.

大多数现代编译器在非 Windows 平台 (gcc) 上都支持这种功能吗?

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

我想避免平台编译问题，但也想避免后备防护的额外工作:

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

我应该担心吗?我应该在这上面花费更多的精力吗?

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

推荐答案

使用 #pragma once 应该适用于任何现代编译器，但我认为没有任何理由不使用标准 #ifndef 包括守卫.它工作得很好.一个警告是 GCC 在 #pragma once">3.4 版.

Using #pragma once 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 #pragma once before version 3.4.

我还发现，至少在 GCC 上，它识别标准的#ifndef 包含守卫并对其进行优化，所以它不应该比#pragma once 慢很多.

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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