[PD] "sorry: only 5 args typechecked; use A_GIMME"

[Chris Chronopoulos]

oh, i see. i thought the argument after A_DEFFLOAT was the default value of
the float. so it's a 0-termination - got it!

On Mon, Feb 13, 2017 at 4:03 AM, IOhannes m zmoelnig <zmoelnig at iem.at>
wrote:

> On 2017-02-12 22:23, Chris Chronopoulos wrote:
> > registered with class_new(..., A_DEFFLOAT) be sufficient for this simple
> > case? this worked for me on 0.43.4; why doesn't it work in 0.47?
> >
>
> oh.
>
> of course Pd can do *that* for you.
> the problem here is, that your code is just bogus:
> class_new() expects a variable number of arguments.
> but in C there is no way to determine the actual number of arguments
> passed to the function.
> So you need to somehow tell the called function when it should stop to
> expect more arguments.
>
> this can either be done by putting that number into one of the
> function-arguments. an example is the `dsp_add()` function. e.g.:
>
>     dsp_add(clip_perform, 4, x, sp[0]->s_vec, sp[1]->s_vec, sp[0]->s_n);
>
> the second argument (4) tells the dsp_add() function that there are 4
> more arguments to come.
>
> alternatively (if the data permits it), you can use a special
> "terminating") element with a magic value (usually this is just NULL);
> the function would then read it's arguments one by one until in
> encounters that special argument, after which it would stop.
> this is the case with the class_new() function. e.g.:
>
>     clip_class = class_new(gensym("clip~"), (t_newmethod)clip_new, 0,
>         sizeof(t_clip), 0, A_DEFFLOAT, A_DEFFLOAT, 0);
>
> the varidiac part is "A_DEFFLOAT, A_DEFFLOAT" and it *must* be
> 0-terminated. so class_new() knows that there are only two (2) more
> valid arguments.
>
> it seems that with your call to class_new(), you were just "lucky" and
> the compiler you used back then with Pd-extended happened to insert a
> NULL value after your A_DEFFLOAT.
> so your statement "this worked for me on 0.43" should actually read:
> "this accidentally happened to work for *me* at some point".
>
> but really you were relying on undefined behaviour, and should just fix
> the original code.
>
> fgamsdr
> IOhannes
>
>
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