Re: strto[u]l and ERANGE

"Eric Sosman" <esosman@xxxxxxxxxxxxxxxxxxx> wrote in message
news:b6adnaHRifghulHfRVn-2Q@xxxxxxxxxxxxxx

> P.J. Plauger wrote:
>
>> "S.Tobias" <siXtY@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote ...
>>> [...] According to my reading of 7.20.1.4 (too long to quote)
>>>in `strtoul("-1", 0, 10)', first "1" is converted
>>>into a (mathematical) value `1'. Then, since there's
>>>a "-", the value is negated (value `-1'). Then a check is made
>>>if the value is representable (0..ULONG_MAX); it is clearly not,
>>>so strtoul should return ULONG_MAX and set `errno' to ERANGE.
>>>Have I got something wrong?
>>
>> Yep, the "it is clearly not" part. Negating an unsigned value
>> is well defined, since "unsigned" really means modulus arithmetic.
>
> Can we conclude that
>
> strtoul("99999999999999999999999999999999999999999"
> "99999999999999999999999999999999999999999"
> "99999999999999999999999999999999999999999"
> "99999999999999999999999999999999999999999"
> "99999999999999999999999999999999999999999"
> "99999999999999999999999999999999999999999",
> NULL, 0)
>
> ... is similarly well-defined, and should not report an out-of-
> range error?
>
> (I'm not being facetious; I'm looking for information.
> The Standard's text seems foggy about such matters.)

No. The converted value must be representable as a value
of the specified unsigned type. Negating a representable
value always yields a representable value; that was the
narrow point I was addressing.

P.J. Plauger
Dinkumware, Ltd.
http://www.dinkumware.com


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