C中的宏的使用(宏嵌套/宏展开/可变参数宏) 原

基本原则：

在展开当前宏函数时，如果形参有#或##则不进行宏参数的展开，否则先展开宏参数，再展开当前宏。

#是在定义两边加上双引号

#define _TOSTR(s) #s

printf(_TOSTR(test ABC))
printf(_TOSTR("test ABC"));
printf(_TOSTR(_TOSTR(test ABC)));

==================
预编译结果：
printf("test ABC")
printf("\"test ABC\"");
printf("_TOSTR(test ABC)");

##是原样代入

 

#define HI_BOY HiBoy!
#define __ORIGINAL(s) s
#define _TOSTR(s) #s
#define STR_CONCAT(x, y) x##y

printf(HI_BOY);
printf(__ORIGINAL(HI_BOY));
printf(_TOSTR(HI_BOY));
printf(_TOSTR(__ORIGINAL(HI_BOY)));
printf(STR_CONCAT(HI_BOY, HI_BOY ));
printf(STR_CONCAT(_TOSTR(HI_BOY), _TOSTR(HI_BOY) ));
===========================================================
预处理后的结果：
printf(HiBoy!);
printf(HiBoy!);
printf("HI_BOY");
printf("__ORIGINAL(HI_BOY)");
printf(HI_BOYHI_BOY);
printf("HI_BOY" "HI_BOY");

连续的两个双引号会被忽略掉

以下写法结果一样：

printf("this is a test sentence. are you ok?\n");
printf("this is a test ""sentence."" are you ok?\n");
printf("this is a test sentence."   " are you ok?\n");
printf("this is a"           " test ""sentence. are"" you ok?\n");

==============
this is a test sentence. are you ok?
this is a test sentence. are you ok?
this is a test sentence. are you ok?
this is a test sentence. are you ok?

嵌套

#define  QUOTATION "
#define HI_BOY HiBoy!
#define __ORIGINAL(s) s
#define _TOSTR(s) #s
#define STR_CONCAT(x, y) x##y

printf(HI_BOY);
printf(__ORIGINAL(HI_BOY));
printf(_TOSTR(HI_BOY));
printf(_TOSTR(__ORIGINAL(HI_BOY)));
printf(STR_CONCAT(HI_BOY, HI_BOY ));
printf(STR_CONCAT( _TOSTR(HI_BOY), _TOSTR(HI_BOY) ));
printf(                  STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) ));
printf(           _TOSTR(STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) )));
printf(_TOSTR(__ORIGINAL(STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) ))));
printf(           ""(STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) ))"");
printf(_TOSTR(__ORIGINAL(STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) ))));
printf(           QUOTATION(STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) ))QUOTATION);
printf(           QUOTATION STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) )QUOTATION);


==================================================
预编译结果：
printf(HiBoy!);
printf(HiBoy!);
printf("HI_BOY");
printf("__ORIGINAL(HI_BOY)");
printf(HI_BOYHI_BOY);
printf("HI_BOY" "HI_BOY");
printf(                  HiBoy!HiBoy!);
printf(           "STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) )");
printf("__ORIGINAL(STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) ))");
printf(           ""(HiBoy!HiBoy!)"");
printf("__ORIGINAL(STR_CONCAT( __ORIGINAL(HI_BOY), __ORIGINAL(HI_BOY) ))");
printf(           "(HiBoy!HiBoy!)");
printf(           " HiBoy!HiBoy! ");

参考

 https://blog.csdn.net/Pillary/article/details/53705158