Re: Is this OK in C++ and C?

[Joe Pfeiffer <pfeiffer@cs.nmsu.edu>]

Jerry Stuckle <jstuckle@attglobal.net> writes:

> On 12/31/2012 7:30 PM, Joe Pfeiffer wrote:
>> Jari Fredriksson <jarif@iki.fi> writes:
>>>>
>>> This is a known bug in Debian GNU/Linux. Happy new year ;)
>>
>> Where does the standard require a warning in this case?  If no warning
>> is required, the behavior is not a bug.
>>
>>
>
> I don't have a copy of the standard any more, but IIRC it does need a
> warning.  It requires a conversion from signed to unsigned, which can
> cause incorrect data (as in this case).
>
> Promotions (i.e. short to int, float to double) will never cause a
> loss of data, and do not require warnings.
>
> But I also admit it's been several years since I looked at the spec
> and my memory isn't what it used to be (at least that's what my wife
> tells me).

Looking into it a bit more, I can't find a place where the C99 standard
requires *any* warnings.  In particular:

                                          Annex I
                                      (informative)
                                  Common warnings
1 An implementation may generate warnings in many situations, none of which are
  specified as part of this International Standard. The following are a few of the more
  common situations.

  (a list of warnings follows)

A search doesn't turn up the string "warn" anywhere in the standard
except in this annex.

(granted, I don't have the final standard, just a draft from 2005.  But
still...)