surround complex macros in ()

daniel watson ozzloy at
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

void main(void){
  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
at runtime?

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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