include - #pragma once 与 #if !defined MYHEADER_INCLUDED_

Question

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Possible Duplicate:
#pragma once vs include guards?

使用 #pragma once 有什么区别(在性能、可用​​性和功能方面)和 #if !defined MYHEADER_INCLUDED_结构体？或者两者有什么区别？

Answer 1

维基百科有你所有的答案，很容易找到

From the article

In the C and C++ programming languages, #pragma once is a non-standard but widely supported preprocessor directive designed to cause the current source file to be included only once in a single compilation.

Thus, #pragma once serves the same purpose as #include guards, but with several advantages, including: less code, avoiding name clashes, and improved compile speed.

它更深入地了解了 article 中的优缺点。 .如果你真的有兴趣，我建议你完整地阅读它，而不仅仅是上面的介绍。