[Ksummit-discuss] [CORE TOPIC] More useful types in the linux kernel

[NeilBrown]

On Fri, Jul 22 2016, Julia Lawall wrote:
>
> In C, enums are ints.  Is there a Gcc option that checks them?  For
> example, the following program compiles fine with -Wall:
>
> enum one {ONE=1, TWO=2, THREE=3};
> enum two {ONEX=7, TWOX=8, THREEX=9};
>
> int f (int x) {
>   enum one o = ONE;
>   enum two t = THREEX;
>   if (x) o = t; else t = o;
>   return 0;
> }

However with this slight change (and line-numbers added for clarity)

     1	
     2	enum one {ONE=1, TWO=2, THREE=3} __attribute((bitwise));
     3	enum two {ONEX=7, TWOX=8, THREEX=9} __attribute((bitwise));
     4	
     5	int f (int x) {
     6	  enum one o = ONE;
     7	  enum two t = THREEX;
     8	  if (x) o = t; else t = o;
     9	  return 0;
    10	}


sparse complains:

/tmp/test.c:8:14: warning: mixing different enum types
/tmp/test.c:8:14:     int enum two  versus
/tmp/test.c:8:14:     int enum one 
/tmp/test.c:8:26: warning: mixing different enum types
/tmp/test.c:8:26:     int enum one  versus
/tmp/test.c:8:26:     int enum two 

Is that what you were hoping for?

NeilBrown
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 818 bytes
Desc: not available
URL: <http://lists.linuxfoundation.org/pipermail/ksummit-discuss/attachments/20160804/35c1efbf/attachment-0001.sig>