Urban Widmark <urban@svenskatest.se> said:
> On Sat, 24 Jun 2000, Tigran Aivazian wrote:
> > K&R says (page 213, A8.3):
> >
> > Adjacent field members of structures are packed into
> > implementation-dependent storage units in an implementation-dependent
> > direction. ... The members of a structure have addresses increasing in
> > the order of their declaration.
> >
> > I think Alan Cox is right - there is no guarantee that field members of a
> > structure can be found one after another starting from the first field.
AFAIU, the "implementation dependent direction" here is big vs
little enedian, at most. See that that _addresses_ are guaranteed to be
increasing. Modulo padding (which in the example below isn't applicable
anywhere I know), they are the same anywhere.
> So all drivers (I'm sure there are a few) that use something like
>
> struct foo {
> u32 a;
> u32 b;
> u32 c;
> u32 d;
> }
>
> to communicate with some hardware (4 32-bit values with addresses in
> sequence) should be fixed not to make assumptions about the layout of a
> struct?
This would break one of the important uses of C (hardware fiddling) big
way.
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This archive was generated by hypermail 2b29 : Mon Jun 26 2000 - 21:00:06 EST