Re: KNF and the C preprocessor

[David Laight <david%l8s.co.uk@localhost>]

On Tue, Dec 11, 2012 at 06:10:09AM +0000, David Holland wrote:
> On Tue, Dec 11, 2012 at 01:27:09AM +0000, Roland C. Dowdeswell wrote:
>  > As an example, I often define a macro when I am using Kerberos or
>  > GSSAPI that looks roughly like:
>  > 
>  > #ifdef K5BAIL(x) do {
>  >            ret = x;
>  >            if (ret) {
>  >                    /* format error message and whatnot
>  >                     * in terms of #x.
>  >                     */
>  > 
>  >                    goto bail;
>  >            }
>  >    } while (0)
> 
> The code like this in src/sys/nfs is a reliably steady source of
> problems, and I'd argue that macros of this form are not at all worth
> the problems they cause.

Absolutely, that is one construct I would ban.
Encapsulating so you can do:
        if (K5BAIL(xxx(....), "error text"))
                goto bail;
Or even separating the function name (so it can be traced)
at least leaves the flow control obvious.
If you embed a goto (or return) in a #define you'd better have the
defininition very close to the use.

        David

-- 
David Laight: david%l8s.co.uk@localhost