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From: Richard Kettlewell <invalid@invalid.invalid>
Newsgroups: comp.lang.c
Subject: Re: The difference between strtol() and strtoul() ?
Date: Sun, 23 Jun 2024 17:39:37 +0100
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gazelle@shell.xmission.com (Kenny McCormack) writes
> Interestingly, I note that strtoul() accepts strings that begin with a
> sign (+ or -).  This is odd, since you'd (*) think that a sign
> (particularly, a minus) would be a syntax error in parsing for an
> unsigned value.
>
> Further, although the (Linux) man page is more than a bit murky on the
> subject, it seems that the result of parsing, say, "-1", with
> strtoul() is the largest unsigned value (usually, 2**N-1 or a lot of
> F's (in hex)).  Whereas, I would expect it to be 1 (i.e., just take
> the absolute value).
>
> Comments?  I find this all very counterintuitive.

I can think of contexts where the string -1 would be read as meaning 1
(e.g. GF(2^n)) but I don’t think most people would think they were a
sensible analogy for stroul behavior. Its behavior seems consistent with
the normal meaning of unary minus (i.e. additive inverse) and of course
with C’s treatment of unsigned integer types.

-- 
https://www.greenend.org.uk/rjk/