On Fri, Dec 05, 2003 at 12:31:40 +0200, Momchil Velikov wrote: > >>>>> "Jan" == Jan Hudec <bulb@ucw.cz> writes: > > Jan> On Tue, Dec 02, 2003 at 15:12:52 -0800, John Tyner wrote: > >> I believe that it is so that gcc will throw a warning if the two types > >> are not compatible. > > Jan> Actualy, it should throw a warning if they are not exactly the same, > Jan> because if they are not, the comparsion breaks aliasing rules. > Jan> Especially it should throw a warning if one is signed and the other is > Jan> not. Well, I've just checked what the warning will actually look like: ,test.c: In function `foo': ,test.c:3: warning: comparison of distinct pointer types lacks a cast (the pointer were signed ** and unsinged ** and that are definitely compatible). > Aliasing rules are NOT like this. See below: > > [#7] An object shall have its stored value accessed only by an lvalue > expression that has one of the following types:73) > > -- a type compatible with the effective type of the object, > > -- a qualified version of a type compatible with the effective type > of the object, > > -- a type that is the signed or unsigned type corresponding to the > effective type of the object, > > -- a type that is the signed or unsigned type corresponding to a > qualified version of the effective type of the object, > > -- an aggregate or union type that includes one of the > aforementioned types among its members (including, recursively, a > member of a subaggregate or contained union), or > > -- a character type. Well, right. signed and unsigned variants can alias and character can alias anything. However, the warning is fortunately generated on exact equality (of efective types). ------------------------------------------------------------------------------- Jan 'Bulb' Hudec <bulb@ucw.cz> -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
