对于在预处理器阶段展开的循环宏？ [英] For loop macro which unrolled on the pre-processor phase?

问题描述

我想用gcc预处理器编写几乎相同的代码声明500次。让我们说出于演示的目的，我想使用宏 FOR_MACRO ：

  #define FOR_MACRO（x）\ 
 #for {1 ... x}中的i：\ 
 const int arr_len _ ## x [i] = {i}; 
  

并呼叫 FOR_MACRO（100）转换为：

  const int arr_len_1 [1] = {1}; 
 const int arr_len_2 [2] = {2}; 
 
 ... 
 
 const int arr_len_100 [100] = {100}; 
  

解决方案

这不是个好主意：

尽管原则上可行，但使用预处理器意味着您必须至少手动展开循环一次，最终会得到一些对循环深度的任意实现定义限制，并且会生成所有语句。

更好地使用您选择的脚本语言生成代码（可能位于单独的可包含文件中），并将其与您的构建过程集成在一起。

p>

I want to use gcc pre-processor to write almost the same code declaration for 500 times. let's say for demonstration purposes I would like to use a macro FOR_MACRO:

#define FOR_MACRO(x) \
    #for i in {1 ... x}: \
        const int arr_len_##x[i] = {i};

and calling FOR_MACRO(100) will be converted into:

const int arr_len_1[1] = {1};
const int arr_len_2[2] = {2};

...

const int arr_len_100[100] = {100};

解决方案

This is not a good idea:

While possible in principle, using the preprocessor means you have to manually unroll the loop at least once, you end up with some arbitrary implementation-defined limit on loop depth and all statements will be generated in a single line.

Better use the scripting language of your choice to generate the code (possibly in a separate includeable file) and integrate that with your build process.

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