bde at zeta.org.au
Sat Nov 15 00:17:16 PST 2003
On Fri, 14 Nov 2003, Jacques Vidrine wrote:
> Bruce Evans said the following on 11/14/03 6:54 PM:
> > I prefer the cast.
> Actually, so do I :-) MIN/MAX values won't work for removing some (IMHO
> stupid) warnings emitted by GCC. So this kind of thing OK?
> long n;
> time_t t;
> errno = 0;
> n = strtoul(...);
> if (errno == ERANGE || (long)(t = n) != n)
> /* out of range */;
Not quite like that. strtoul() returns an unsigned long whose value may
be lost by assigning it to a plain long. Mixtures of signed and unsigned
types are tricky to handle as usual. Suppose we make n unsigned long
and it has value ULONG_MAX, and time_t is long, then (t = n) == n,
but t doesn't actually represent n (casting (t = n) to long or unsigned
long doesn't help). So it seems to be necessary to be aware that time_t
is signed and either use strtol() initially or check that t >= 0 if
n is unsigned long. If time_t is actually signed then we may get a GCC
warning for this check...
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