Jacques Vidrine nectar at freebsd.org
Sat Nov 15 05:04:01 PST 2003

Bruce Evans said the following on 11/15/03 2:17 AM:
> On Fri, 14 Nov 2003, Jacques Vidrine wrote:
>>  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...

Doh, sorry, that's a typo.  I meant strtol (which is what is currently
used in the relevant portion of libc--- strptime.c, BTW).  Negative
values must be allowed here.

Jacques Vidrine   NTT/Verio SME      FreeBSD UNIX       Heimdal
nectar at celabo.org jvidrine at verio.net nectar at freebsd.org nectar at kth.se

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