[DGD] Re: varargs int ...

[Erwin Harte]

On Sat, Feb 21, 2004 at 03:04:16AM -0500, Michael McKiel wrote:
> Is it possible to test if a varargs int parameter was passed to a given
> function or not?
> I was playing around with a strstr() function, and seems I want to make it
> work differently if the 2nd int variable wasn't passed ie:
> string strstr(string str, int start, varargs int end) {
> 
> if I don't pass it 'end' then the function should assume end = strlen(str)-1
> if I pass it end == 0, then it should return a nil string, since it would be
> a zero length string.
> But it seems all I can test for is !end
> and that is true if I don't pass an end variable, and IF I pass it 0...
> 
> So what am I missing?

The only way I can see to be 100% sure what parameters were provided
or not, is by using the ellipsis:

    string strstr(string str, int start, varargs mixed extra...) {
        int end;

        if (sizeof(extra) == 0) {
            /* No extra parameters provided. */
        } else if (sizeof(extra) == 1 && typeof(extra[0]) == T_INT) {
            /* Extra parameter was provided and was an integer. */
            end = extra[0];
        } else {
            error("bad argument 3 to strstr");
        }
        ...
    }

The next best thing is:

    string strstr(string str, int start, varargs mixed end) {
        if (end == nil) {
            /* Varargs parameter omitted or 'nil' value used. */
        } else if (typeof(end) == T_INT) {
            /* Extra parameter provided and was an integer. */
        } else {
            error("bad argument 3 to strstr");
        }
        ...
    }

But then you can't distinguish between strstr("foo", 1, nil) and
strstr("foo", 1).

If you don't care about that distinction, then by all means go ahead
and use that approach. ;-)

Hope that helps,

Erwin.
-- 
Erwin Harte <harte at is-here.com>
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