🚀 go-pugleaf

rhl@grendel.Princeton.EDU (Robert Lupton the Good) writes:


>   const int i = 0;
>
>   (int)i = 1;				/* Fails */
>   *(int *)&i = 1;			/* OK */
       
>Thinking about ROMs my guess is that gcc and the IBM xlc compilers are
>correct to reject the former assignment, and that their acceptance of
>the latter is permitted, but could anyone comment? 

The first assignment is illegal because a cast yields a value, not
an lvalue, and you may not assign to a value.  It has nothing to do
with const.

The second assignment assigns to an object via a modifiable lvalue, and
so violates no constraint.  Nonetheless, the results of assigning to an
object declared const via a non-const lvalue are undefined.  (ANSI 3.5.3)

You can't rely on any particular result.  The compiler is not obliged
to diagnose the problem, but may do so.  The resulting code might do
what you intended, but need not.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com
Vice Chair, ANSI C++ Committee, X3J16