-=> On 02 Jul 96  21:34 you wrote to me <=-

Hi Paul,

PE> The mktime() example shows a comparison to -1 instead of
PE> (time_t)-1, which could cause problems on certain
PE> implementations (theoretical).

MS> I expect that it could, but I think you may need to explain the
MS> scenario to me.  I suppose that if time_t was an extra wide
MS> integral type then there could be problems analogous to char c =
MS> getchar().

PE> If time_t is an unsigned short, on a system where sizeof short <
PE> sizeof int, then the time_t return of 0xffff will be converted
PE> to 0x0000ffff (e.g.) and not compare equal to 0xffffffff which
PE> is what "-1" is.

Of course!  Promotion from unsigned to signed can be dangerous.  I
notice in another message you're discussing the changes in the
promotion rules.  When in doubt, I refer to K&R2, because I find it
hard to keep the details in my head.  I think this is partly because
I started writing C in 1980 & I learned the old rules first.

Michael Stapleton of Graphic Bits.

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