Leopold Toetsch wrote:
On Oct 30, 2005, at 1:54, Nick Glencross wrote:
Quick question...
I've been looking through inter_run and extend to see how to pass
arguments to a parrot method/function from C, but all the prototypes
that I've seen have '...' or 'va_list' to accept the arguments.
If I don't know what the arguments or their respective types are at
compile time, what function is best for me?
There are 2 cases here:
1) you know the amount of args
2) you don't
In both cases you can use Parrot_runops_fromc_args() with a signature
of "vPPP" or "vP" respectively.
If you expect a return value change the initial 'v' to 'P'. For the
second case you have to put all args into a *PMCArray.
Hmmm. still don't think that's what I want. Obviously this is in the
context of the NCI callback stuff that I'm looking into -- no surprises
there.
The callback is written by the parrot coder, so let's say we have this:
.sub _call_back
.param int a
.param int b
print "Hello world!\n"
print a
print " "
print b
print_newline
.end
The callback 'trampoline' code in C needs to call this, but doesn't know
at compile time what to expect, but it does have the parrot signature
(e.g. vii) and access to all the values to be passed on, albeit only by
looping over them.
For case 1) I have the number of args and the signature, but don't
believe that I can convert the arguments into a form that I can pass to
any of the existing function calls.
In case 2), which I've just tried, I think that I'm right in saying that
the *PMCArray will arrive as the first argument of _call_back, which
will automagically convert to an int, being its length.
What think is needed is a routine which will dereference the array and
pass its contents as arg1, arg2, ...
Thanks for your help Leo! As you can imagine this is the last step to
having something to show for callbacks!
Nick
