surround complex macros in ()
ozzloy at challenge-bot.com
Thu Aug 26 01:21:44 EDT 2021
let me know if this is the right place to ask.
i recently tried to make a commit adding parentheses around a macro
it was rejected as "This is not a real change that is needed."
at first, i thought this meant that the code would be identical with and
without parentheses surrounding a complex macro's definition, when the
macro is just typecasting an expression. but then i came up with code
where having parens or not changes the meaning of the code.
#define with ((int)a)
#define sans (int)a
int b = 0;
$ gcc -o delete-me delete-me.c
delete-me.c: In function ‘main’:
delete-me.c:7:7: error: lvalue required as increment operand
7 | with++;
the compiler complains about the macro defined with parentheses, and
does not have a problem with the other macro defined sans parentheses.
this is only a compile time difference, and maybe that's the only
possible difference that could be made by the parentheses.
i'm curious if there's a way to know for sure that there exists no
possible expression with such a macro in it that would cause a more
subtle difference. for example, how do i rule out the possibility
that the code could compile and have a different value than expected
as a side note, i signed up for the kernelnewbies mailing list, and i do
not see any messages in my inbox, except a reply to a message i sent
out. i checked here
in some expression
and do not see the message i sent, or the reply to it.
am i seeing the right thing? did i sign up correctly? is that the
right page to view the mailing list messages online?
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