如何在预处理程序#if条件中捕获未定义的宏? [英] How to catch undefined macro in preprocessor #if condition?

问题描述

基于此问题如何捕获空的已定义gcc宏?我还有另一个问题.如何在预处理器 #if 条件下捕获未定义的宏?示例代码:

Based on this question How to catch empty defined macro with gcc? I have another problem. How to catch undefined macro in preprocessor #if condition? Example code:

#include <stdio.h> 

int main()
{
#if ENABLE_SOMETHING == 1
    ... do something ..
#endif
 return 0;
}

当未使用gcc编译器设置了 ENABLE_SOMETHING 时(是否有些标志)，是否存在一种捕获错误/警告的方法?或者也许我可以使用外部工具?

Is there a way to catch error/warning when ENABLE_SOMETHING is not set using gcc compiler(maybe some flag)? Or maybe there are external tools which I can use?

我知道我可以写这样的东西:

I know than i can write something like this :

#ifndef ENABLE_SOMETHING
    #error "ENABLE_SOMETHING undefined!"
#endif

但是我在代码中有很多不同的定义( ENABLE_STH1 ， ENABLE_STH2 ， ENALBE_STH3 ...等)，我没有不想手动解决此问题.我正在为我们的项目寻找一些自动解决方案.

But I have a huge amount of different defines(ENABLE_STH1, ENABLE_STH2, ENALBE_STH3 ... etc.) in code and i don't want to fix this manually. I'm looking for some automatic solution for our project.

推荐答案

当未设置ENABLE_SOMETHING时是否有一种捕获错误/警告的方法使用gcc编译器(也许有一些标志)?

Is there a way to catch error/warning when ENABLE_SOMETHING is not set using gcc compiler(maybe some flag)?

使用GCC，您可以使用 -Wundef 标志.

With GCC you can use the -Wundef flag.

摘自官方文档

-Wundef

-Wundef

警告是否在#if指令中评估未定义的标识符.此类标识符将替换为零.

Warn if an undefined identifier is evaluated in an #if directive. Such identifiers are replaced with zero.

例如，此C代码:

#include <stdio.h>

int main(void)
{
#if UNDEFINED_MACRO
  printf("hi mum!\n");
#endif

  return 0;
}

...使用GCC编译，-Wundef标志产生以下结果:

... compiled with GCC and the -Wundef flag yields this:

$ gcc undef.c -Wundef
undef.c: In function 'main':
undef.c:5:5: warning: "UNDEFINED_MACRO" is not defined [-Wundef]
 #if UNDEFINED_MACRO
     ^

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