C 预处理器宏扩展 [英] C pre-processor macro expansion

问题描述

我正在尝试做(我本来以为的)是一个简单的宏扩展

I'm trying to do (what I would have thought) was a simple macro expansion

#define CLEAR_DIGIT(a,b)    iconMap[a] &= ~(b)
#define R1 4, 16
CLEAR_DIGIT(R1);

现在我希望它扩展为 CLEAR_DIGIT(4,16) 扩展为 iconMap[4] &= ~16但是，它没有...如果我将 CLEAR_DIGIT 设为函数:

Now I would expect that to expand to CLEAR_DIGIT(4,16) which expands to iconMap[4] &= ~16 However, it doesn't... If I make CLEAR_DIGIT a function:

void ClearDigit(unsigned char a, unsigned char b)
{
    iconMap[a] &= ~b;
}
#define R1 4, 16
ClearDigit(R1);

然后它工作正常，因此将 R1 扩展到两个参数不是问题......有没有办法在执行宏函数扩展之前强制它扩展 R1?

then it works fine, so R1 being expanded out to the two arguments isn't an issue... Is there any way of forcing it to expand R1 before doing the macro function expansion?

推荐答案

你可以使用辅助宏.另请参阅双字符串化问题

You could use a helper macro. See also double-stringize problem

#define CLEAR_DIGIT_HELPER(a,b) iconMap[a] &= ~(b)
#define CLEAR_DIGIT(x) CLEAR_DIGIT_HELPER(x)
#define R1 4, 16
CLEAR_DIGIT(R1);

这篇关于C 预处理器宏扩展的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！