C ++预处理器如何工作？ [英] How does C++ preprocessor work?

问题描述

我正在阅读《 C ++ Primer》第5版，我读到预处理器是在C ++编译器之前运行的程序，并用适当的内容替换＃include，＃define和#ifdefs等，然后进行控制交给编译器。

I am reading the book "C++ Primer" 5th Edition and I read that the preprocessor is a program that runs before the C++ compiler and replaces the #include, #define and #ifdefs and others with the appropriate content and then transfer control over to the compiler.

但是我在cl.exe（Microsoft编译器）中遇到了一种方法，可以查看直接保存到文件中的预处理器输出。我做到了，当我打开预处理器输出文件时，我感到很惊讶，因为我没有找到我所期望的！

But I came across a way in cl.exe (Microsoft Compiler) to view the preprocessor output saved directly to file. I did it, and when I opened the preprocessor output file I was surprised because I did not find what I expected!

它们很大，并且包含看起来很模糊的代码！

They were totally big and contained what looked like obfuscated code!

请解释一下C ++的预处理器实际上是做什么的。

推荐答案

完全可以像处理C或C ++一样预处理Java。只需使用以下内容：

It is entirely possible to pre-process Java just like you do C or C++. Just use something like this:

gcc -E myjava.java > myjava.preprocesses.java

然后可以使用宏扩展， #if 等内容。当然，它确实具有缺点，那就是需要另外的工具进行编译。

Then you can use macro expansion, #if etc to your hearts content. Of course, it does have the drawback that there is a further tool needed for the compile.

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