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

[Tixy <tixy@yxit.co.uk>]

On Tue, 2013-01-01 at 11:41 -0700, Joe Pfeiffer wrote:
> 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.

But it probably has quite a few occurrences of 'diagnostic', the C++
standard does; and it states that a 'diagnostic message' shall be issued
if a program breaks the rules of the language except where the standard
explicitly states no diagnostic is required.

With regard to the original question of assigning a negative value to an
unsigned integer, this seems to be allowed and defined behaviour. The
section on integral conversions has:

        If the destination type is unsigned, the resulting value is the
        least unsigned integer congruent to the source integer (modulo 2
        n where n is the number of bits used to represent the unsigned
        type). [Note: In a two’s complement representation, this
        conversion is conceptual and there is no change in the bit
        pattern (if there is no truncation). ]
        
-- 
Tixy