＃定义的整个图书馆的范围？ [英] #Define's scope throughout library?

问题描述

说我有一个恒定的：

#define PI 3.14

说我有多个头文件和源文件的静态库。如果我宣布这个头文件，将其适用范围适用于所有的源文件？或做源文件需要包括 PI ？

推荐答案

他们将需要包括其中包含的#define PI 3.14文件，否则preprocessor不会读的#define线，随后编译会失败。

They will need to include the file which contains #define PI 3.14, otherwise the preprocessor will not read the #define line, and subsequently the compile will fail.

在C ++中，一个很好的方式去思考编译过程中是每一个人的C ++文件是通过一个preprocessor，这需要所有的#define，＃包括第​​一次运行时，和其他preprocessor声明，并取代他们在整个code，然后编译（在这一点上，C ++的文件和任何通过的#include带来了处理仿佛它们是一个非常大的单个文件），然后在这之后，一个连接器会在最终输出preprocess /编译阶段，所有的C ++文件，并把它们组装成一个最终输出文件。在preprocessor（它处理定义）编译阶段之前的作品，不联动期间。

In C++, a good way to think of the compile process is that each individual C++ file is first run through a preprocessor, which takes all the #define, #include, and other preprocessor statements and replaces them throughout the code, then compiled (at this point, the C++ file and anything brought in via #include treated almost as if they were one very large single file), then after that, a linker takes the final output of the preprocess/compile stage for all of the C++ files and assembles them into one final output file. The preprocessor (Which handles the defines) works before the compile stage, not during linkage.

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