Macro expansion in the C language

 #include <stdio.h> #define  F (A, b) a# #b  #define  g (a) #a  #define  H (a) g (a) int   Main () {printf ( "  %s\n  , H (f (1 , 2    %s\n  , G (F (1 , 2     return  0  ;}

How to expand the rules for a macro function: when the current macro function is expanded, if the parameter has # or # #则不进行宏参数的展开, expand the macro argument first, and then expand the current macro.

The Almighty StackOverflow

Http://stackoverflow.com/questions/1686324/how-does-this-c-code-work
Http://stackoverflow.com/questions/4364971/and-in-macros

http://zjf30366.blog.163.com/blog/static/411164582009061075923/

Analysis:

x# #y把两个符号连起来 XY
#a指把a当成符号 is to think of the string behind the #

#define F (A, B) a# #b # define G (a)   #a # define H (a)  g (a)

printf ("%s\n", H (f ()));   Results 12
Because the argument in the H macro is another macro with # #, the macro as a parameter is not expanded

printf ("%s\n", G (f)));   Results f (+)
Because the argument in the G macro is another macro, but without # #, the macro as a parameter expands first

When you expand the current macro function, if the parameter has a # or # #则不进行宏参数的展开, expand the macro argument first, and then expand the current macro.

Macro expansion in the C language