C预处理器标记化不扩展宏吗? [英] C preprocessor tokenization does not expand macro?
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问题描述
1)为什么在以下表达式中不扩展宏MSG?
1) Why is the macro MSG not expanded in the following expression?
#define MSG Hello
#define HELLO(name) MSG ## name
void HELLO(Dave) () {}
使用
gcc -E -P test.cpp
输出:
void MSGDave () {}
MSG名称
扩展为 Hello Dave
。并且 MSG#名称
扩展为 Hello Dave
。那么是什么原因导致gcc无法扩展 MSG ##名称
?
MSG name
expands to Hello Dave
. And MSG # name
expands to Hello "Dave"
. So what causes gcc not to expand MSG ## name
?
2)是否有解决方法?
2) Is there a workaround?
是否存在像define(x)这样的预处理指令,例如expand(x)?
Is there a preprocessor directive like defined(x), such as expand(x)?
推荐答案
#define MSG Hello
#define cat(x, y) x ## y
#define cat2(x, y) cat(x, y)
#define HELLO(name) cat2(MSG,name)
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