C语言 C 宏：#if 检查相等性
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C macro: #if check for equality
提问by anon
Is there a way to do check for numerical equality in macros?
有没有办法检查宏中的数值相等性？
I want to do something like
我想做类似的事情
#define choice 3
#if choice == 3
....
#endif
#if choice == 4
...
#endif
Does C macros have support for things like this?
C 宏是否支持这样的事情？
回答by David R Tribble
Another way to write your code uses chained #elifdirectives:
另一种编写代码的方法是使用链式#elif指令：
#if choice == 3
...
#elif choice == 4
...
#else
#error Unsupported choice setting
#endif
Note that if choiceis not #defined, the compiler (preprocessor) treats it as having the value 0.
请注意，如果choice不是#defined，则编译器（预处理器）将其视为具有值0。
回答by wallyk
Indeed that should work. See http://gcc.gnu.org/onlinedocs/cpp/If.html#If
确实应该可以。见 http://gcc.gnu.org/onlinedocs/cpp/If.html#If
That reference is accurate, but written in "standards format": abstractly without examples.
该参考是准确的，但以“标准格式”编写：抽象地没有示例。
回答by Nicolas Guillaume
As far as i know that should work. What compiler are you using ?
据我所知，这应该有效。你用的是什么编译器？
PS : Just for information, the defines names are usually written in caps !
PS：仅供参考，定义名称通常用大写！
#define CHOICE 3
#define CHOICE 3
