Re: Returning a pike array from C

"Felip Alàez Nadal" <uu.nix.uu <at> gmail.com> wrote:

> /.../ I've a problem, because the lu method has to return a pike
> array with 4 elements: 3 Math.Matrix objects which I've created
> inside the method and an int. Could someone explain me how to create
> a pike array from the C API and return It?

Easiest is to use the svalue stack; there are numerous examples
throughout the C sources. It goes something like this:

  push_object (matrix_obj_1);
  push_object (matrix_obj_2);
  push_object (matrix_obj_3);
  push_int (the_integer);
  f_aggregate (4); /* Make an array of the 4 top elements on the stack. */

The array is left on the top of the stack and will become the return
value if you return afterwards.

Note that it's vital to keep track of the ref counts in cases like
this (actually, always when pike objects are handled in C). Depending
on your situation, you should use either push_object (which doesn't
add a ref to the object) or ref_push_object (which does).

Normally when preparing return values, the non-"ref_" variety is
better since you don't want to keep the object after the return. Thus
you can let the stack "take over" the ref you got somewhere else
(typically in a local variable).

If you make too few refs, you'll get a fatal error or segfault pretty
soon (the error will typically be more obvious if you have a pike
compiled with the --with-rtldebug configure option).

If you make too many refs you'll get permanent garbage instead, which
is more difficult to spot. To avoid that I recommend you use the
--with-cleanup-on-exit configure option that'll give you a leak report
on exit.

> Also, which is the signature which I must declare for pike
> understanding the method?

Well, the pike type is array(Math.Matrix|int), of course. Fixing the
corresponding C code for that is handled for you if you're writing a
.cmod. Aren't you?