我是否应该仍然使用#include警卫和#pragma一次? [英] Should I still use #include guards AND #pragma once?

问题描述

http://en.wikipedia.org/wiki/Pragma_once
当所有这些编译器均支持#pragma once时，我仍应使用include防护吗?
关于堆栈溢出的许多响应都说要同时使用这两种兼容性，但是我不确定这是否仍然正确. 当今哪些编译器不支持#pragma once?

http://en.wikipedia.org/wiki/Pragma_once
Should I still use include guards when all of these compilers support #pragma once?
A lot of responses on stack overflow say to use both for compatibility, but I'm not sure if that still rings true. What compilers today don't support #pragma once?

我不确定同时使用这两种方法是否只是推荐，否则是否仍然有很好的理由使用这两种方法.
仅在使用#pragma once时会引起问题的任何示例吗?

I am not sure if using both was just a recommendation before it became widley adopted, or if there are still very good reasons to use both methods.
Any examples of when only using #pragma once will cause problems?

推荐答案

这取决于程序的可移植性.

It depends on how much portable your program is expected to be.

只要编写的程序可以与肯定支持#prama once的编译器一起使用，只需使用#pragma once就足够了.但是这样做会限制您的程序使用支持实现定义功能的编译器集.

As long as you are writing a program which is supposed to work with compilers which you know definitely support #prama once, just using #pragma once should suffice. But doing so you restrict your program to set of compilers which support the implementation defined feature.

如果您需要程序在所有编译器上运行，则应使用#pragma once并同时包含防护.

If you need your program to work on all compilers then you should use #pragma once and include guards both.

如果编译器不支持#pragma once，它将简单地忽略它 ^[Ref#1] ，在这种情况下，标题保护将达到您的目的，因此使用它们没有错当您不了解目标编译器支持的功能时，都可以使用.

In case a compiler does not support #pragma once it will simply ignore it^[Ref#1], in such a case the header guards will serve you the purpose, so nothing wrong in using them both when you are not aware of features supported by your target compilers.

因此，如果您希望程序在不同的编译器上具有100％的可移植性，那么理想的方法仍然是仅使用包含保护.正如@CharlesBailey正确指出的那样，由于#pragma once的行为是由实现定义的，因此未知编译器上的行为可能会对您的程序产生不利影响.

So if you want your program to be 100% portable on different compilers the ideal way is still to use only the include guards. As @CharlesBailey rightly points out since the behavior for #pragma once is implementation defined, the behavior on an unknown compiler might have a detrimental effect on your program.

^[Ref#1]
标准C ++ 03:16.6 Pragma指令

形式的预处理指令

A preprocessing directive of the form

# pragma pp-tokensopt new-line

使实现以实现定义的方式运行. 该实现无法识别的所有杂注都将被忽略.

causes the implementation to behave in an implementation-defined manner. Any pragma that is not recognized by the implementation is ignored.

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