C头后卫 [英] C include guard

问题描述

在 file1.c中包括 inc.h （含包括后卫的#ifndef INC_H ）的第一次，执行的#define INC_H 。但是现在，当另一个 file2.c中包含相同的 inc.h ，是宏 INC_H 已定义的，它所有的同样的故事和previous定义不在这里繁殖？

解决方案

  

但现在，当另一file2.c中包括相同inc.h，已定义的宏INC_H，

是和否这要看情况。

• 如果 file2.c中包括一些头，其中包括 inc.h 和是， INC_H 已经为 file2.c中定义。这是列入任何级别如此。




• 否则，否尚未确定。

护罩$ P从​​被包括在一个文件中，直接或间接地$ pvent头，不止一次！

When file1.c includes inc.h (containing the include guard #ifndef INC_H) for the first time, the #define INC_H is performed. But now, when another file2.c includes the same inc.h, is the macro INC_H already defined, all it's the same story and previous definition is not propagated here?

解决方案

But now, when another file2.c includes the same inc.h, is the macro INC_H already defined,

Yes and No. It depends.

• If file2.c includes some header which includes inc.h, then yes, INC_H is already defined for file2.c. This is true for any level of inclusion.

• Else, no it is not already defined.

Guards prevent header from being included in a file, indirectly or directly, more than once!

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