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 >>> Signed-off-by: Ian Abbott >> >> 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 --