Hi Ian, On 12/9/22 20:28, Ian Abbott wrote:
On 09/12/2022 18:59, Alejandro Colomar wrote:On 12/8/22 13:34, Ian Abbott wrote:The `scanf()` function does not intentionally set `errno` to `ERANGE`. That is just a side effect of the code that it uses to perform conversions. It also does not work as reliably as indicated in the 'man' page when the target integer type is narrower than `long`. Typically (at least in glibc) for target integer types narrower than `long`, the number has to exceed the range of `long` (for signed conversions) or `unsigned long` (for unsigned conversions) for `errno` to be set to `ERANGE`. Documenting `ERANGE` in the ERRORS section kind of implies that `scanf()` should return `EOF` when an integer overflow is encountered, which it doesn't (and doing so would violate the C standard). Just remove any mention of the `ERANGE` error to avoid confusion.Fixes: 646af540e467 ("Add an ERRORS section documenting at least some of the errors that may occur for scanf().")Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx> Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>I see. How about saying something like "it may also fail for any of any errors that functions used to perform the conversions may fail"?It depends what you mean by "fail". These errors do not make scanf return EOF.
Just to clarify. Does scanf(3) _never_ fail (EOF) due to ERANGE? Or is it that ERANGE sometimes makes it fail, sometimes not?
If it's the former, I agree with your patch. When a function hasn't reported failure, errno is unspecified.
If it's the latter, I'd write something about it.
Technically, the behavior is undefined if the result of the conversion cannot be represented in the object being assigned to by scanf. (In the case of glibc, that probably results in either the integer object being set to a truncated version of the input integer, or the integer object being set to a truncated version of LONG_MIN or LONG_MAX, depending on the actual number.)
Hmm, UB. Under UB, anything can change, so error reporting is already unreliable. If EOF+ERANGE can _only_ happen under UB, I'd rather remove the paragraph. Please confirm.
Setting errno to 0 before calling scanf and expecting errno to have a meaningful value when scanf returns something other than EOF is bogus usage.
Yep, that's bogus. Cheers, Alex -- <http://www.alejandro-colomar.es/>
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