__TIME_MIN/__TIME_MAX

[Bruce Evans]

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...

Bruce