let me know if this is the right place to ask. i recently tried to make a commit adding parentheses around a macro value. https://lore.kernel.org/linux-staging/20210817043038.GA9492@xxxxxxxxxxxxxxxxx/ 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. -------delete-me.c-------- #define with ((int)a) #define sans (int)a void main(void){ int b = 0; with++; sans++; } -------delete-me.c-------- -------terminal-------- $ 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++; | ^~ -------terminal-------- 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 http://lists.kernelnewbies.org/pipermail/kernelnewbies/ 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? thanks! _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
