C 预处理器和操作顺序 [英] C preprocessors and order of operations

问题描述

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.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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