Re: A question about macro replacement

[Brooks Moses <brooks dot moses at codesourcery dot com>]

zhao_bingfeng@topsec.com.cn wrote:
> With following code:
> [CODE]
> struct B {
> 	int c;
> 	int d;
> };
>
> #define X(a, b, c) \
> do\
> {\
> 	if (a)\
> 		printf("%d, %d\n", b.c, c);\
> 	else\
> 		printf("%d\n", c);\
> }while(0);
> [/CODE]
>
> Why
> 	int d = 24;
> 	X(1, b, d);
> can be compiled successfully but
> 	X(1, b, 24);
> not.
>
> I cannot find any description about this behavior in C standard.

Well, with the X(1, b, 24) case, the b.c in the first printf line 
becomes b.24, which is obviously a syntax error.

This sort of thing would be a fair bit easier to track down if you 
quoted the error message rather than just saying that it cannot be 
compiled successfully.

- Brooks