macro特殊用法

#的使用方法（因为老是忘，所以记录于此）:

Quoting macro arguments(当字符串引用)

#define QUOTEME(x) #x

the code

printf("%s\n", QUOTEME(1+2));

will expand to

printf("%s\n", "1+2");

Token concatenation（Token当做字符串连接）

#define MYCASE(item,id) \
case id: \
  item##_##id = id;\
break
 
switch(x) {
    MYCASE(widget,23);
}

The line MYCASE(widget,23); gets expanded here into

case 23:
  widget_23 = 23;
break;

Standard predefined positioning macros

// debugging macros so we can pin down message origin at a glance
#define WHERESTR  "[file %s, line %d]: "
#define WHEREARG  __FILE__, __LINE__
#define DEBUGPRINT2(...)       fprintf(stderr, __VA_ARGS__)
#define DEBUGPRINT(_fmt, ...)  DEBUGPRINT2(WHERESTR _fmt, WHEREARG, __VA_ARGS__)
//...
 
  DEBUGPRINT("hey, x=%d\n", x);

或者：
#define DEBUGPRINT2(args...)  fprintf(stderr, ## args)  //注意args与##之间有空格，特殊用法