[TUHS] Re: Minimum Array Sizes in 16 bit C (was Maximum)

[Ralph Corderoy <ralph@inputplus.co.uk>]

Hi Doug,

> > > > malloc(0) isn't undefined behaviour but implementation defined.
> > >
> > > In modern C there is no difference between those two concepts.
>
> There certainly is a difference, but in this case the practical
> implications are the same: avoid malloc(0).

Many programs wrap malloc() in some way, even if it's just to exit on
failure, so working around malloc(0) is easy enough.

    void *saneloc(size_t size) {
        void *p = malloc(size);
        if (p || size)
            return p;

        return malloc(1);
    }

> In the middle is the default signedness of chars, which generally may
> be mitigated by explicit type declarations.

Similarly, the signedness of an ‘int i: 3’ bit-field.

     (1) Whether a "plain" int bit-field is treated as a signed int
         bit-field or as an unsigned int bit-field (6.7.2, 6.7.2.1).

> Is there any other C construct that implementation-definedness renders
> useless?

There's the '-' in "%[3-7]" for fscanf(3).

    (35) The interpretation of a − character that is neither the first
         nor the last character, nor the second where a ^ character is
         the first, in the scanlist for %[ conversion in the fscanf or
         fwscanf function (7.23.6.2, 7.31.2.1).

-- 
Cheers, Ralph.