请教C语言中的宏

__slucx__

C里宏中如果出现了强转，

1. 
   
2. #define N ((unsigned char) 8)
   
3. 
   
4. #if (N == 8)
   
5. ...
   
6. #endif
   

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这样用就会出现编译错误，
请问为啥会这样？

cokeboL

回复 1# __slucx__

1. #if (N == 8)
   
2. 
   
3. 改成
   
4. 
   
5. #if equal(N, 8)
   
6. 
   
7. “==”应该是语言本身的，不是预编译指令，你在#if 的预编译里用当然不认识
   
8. 
   

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crazy_snail

预编译应该不能识别类型转换吧
求#if值的时候遇到unsigned char会报错

socay2

pmerofc 发表于 2013-01-06 11:18
回复 1# __slucx__

C11 又冒出来了，我咋还在看C89，极度 out 呀！

__slucx__

谢谢各位

C11 又冒出来了，我咋还在看C89

话说我木有看过C标准

sonicling

C++11：

After all replacements due to macro expansion and the defined unary operator have been performed, all remaining identifiers and keywords, except for true and false, are replaced with the pp-number 0, and then each preprocessing token is converted into a token. The resulting tokens comprise the controlling constant expression which is evaluated according to the rules of 5.19 （常量表达式） using arithmetic that has at least the ranges specified in 18.3 （数字限定）. For the purposes of this token conversion and evaluation all signed and unsigned integer types act as if they have the same representation as, respectively, intmax_t or uintmax_t (18.4).

socay2

pmerofc 发表于 2013-01-06 11:36
回复 5# socay2

现在实际编程中用 C11 或 C99 多不？