什么是真正的#include做？ [英] What does #include actually do?

问题描述

在C（或基于C语言），可以愉快地使用下面的语句：

In C (or a language based on C), one can happily use this statement:

#include "hello.h";

和瞧，每一个函数和变量 hello.h 是自动可用的。

And voila, every function and variable in hello.h is automagically usable.

但什么是它实际上做什么？我通过编译文档和教程看了看，花了一些时间在网上搜索，但唯一的IM pression我能形成与神奇的#include 命令它复制膏 hello.h 的内容，而不是该行。有一定有比这更多。

But what does it actually do? I looked through compiler docs and tutorials and spent some time searching online, but the only impression I could form about the magical #include command is that it "copy pastes" the contents of hello.h instead of that line. There's gotta be more than that.

推荐答案

逻辑上，复制/粘贴到底是什么情况。恐怕没有任何更给它。你并不需要在; ，虽然

Logically, that copy/paste is exactly what happens. I'm afraid there isn't any more to it. You don't need the ;, though.

您具体的例子是规范，部分覆盖的 6.10.2源文件包含，第3段：

Your specific example is covered by the spec, section 6.10.2 Source file inclusion, paragraph 3:

形式的preprocessing指令

A preprocessing directive of the form

＃包括 的 Q-字符序列 的新行的

由分隔符之间的指定序列标识的源文件的全部内容导致替代品，指令。

causes the replacement of that directive by the entire contents of the source file identified by the specified sequence between the " delimiters.

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