c语言预处理代码--含括多种知识

#include

/* #if #elif #endif */
#ifndef SET_LINE100
#define SET_LINE100

#line 100

#elif
//
#else
//
#endif

#if 0

#else

#define PRINTX(x) printf(#x" = %d\n", x);
#define cat2(x, y) x ## y
#define xcat2(x, y) cat2(x, y)

#endif

int main(void)
{
 int i = 1;
 
 printf("file :%s Line :%d Date :%s Time :%s Std:%d\n",
   __FILE__, __LINE__, __DATE__, __TIME__, __STDC__);
 #if 0
 ;
 #else
 
 PRINTX(i);
 printf("%f\n", xcat2(cat2(1, 0), 2.3));
 #endif
 
 return 0;
}