C 预处理器和操作顺序
我正在学习C,但我不明白这一点:
I'm learning C, but I do not understand this:
#define square(x) x*x
a = square(2+3) //a = 11
运行时,为什么 a
最终会变成 11
?
When this is run, why does a
end up being 11
?
推荐答案
展开为2+3*2+3
,相当于2+(3*2)+3代码>.使用括号来修复它:
It expands to 2+3*2+3
, which is equivalent to 2+(3*2)+3
. Use parentheses to fix it:
#define square(x) ((x)*(x))
现在用 square(x++)
试试,你会遇到更多问题(未定义的行为).如果可以,请避免将其作为宏执行.
Now try it with square(x++)
and you'll run into more problems (undefined behavior). Avoid doing this as a macro if you can.
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