编译阶段打印宏内容

//两个用于测试的宏
#define PI 3.1415926
#define MAX(a,b) (a)>(b) ? (a) :(b)

//首先定义两个辅助宏
#define   PRINT_MACRO_HELPER(x)   #x
#define   PRINT_MACRO(x)   #x"="PRINT_MACRO_HELPER(x)

//编译阶段打印宏内容
#pragma message(PRINT_MACRO(PI))
#pragma message(PRINT_MACRO(PI2))
#pragma message(PRINT_MACRO(MAX(a,b)))
#pragma message(PRINT_MACRO(MAX(x,y)))

结果输出
note: #pragma message: PI=3.1415926  
//PRINT_MACRO中的两个x都被替换为PI，PRINT_MACRO_HELPER中的#x替换为宏PI的内容
note: #pragma message: PI2=PI2          
//PI2不存在的情况下PRINT_MACRO_HELPER将#x换做PI2
note: #pragma message: MAX(a,b)=(a)>(b) ? (a) :(b)
note: #pragma message: MAX(x,y)=(x)>(y) ? (x) :(y)