Re: [ns] passing lists in pkt header between C++ and OTcl

[Haobo Yu <haoboy@isi.edu>]

> The list can consist of nothing, one number, or a list of numbers.  I know
> how to create this in OTcl.  The problem is when I call the 'recv'
> function in C++ space.  If the OTcl list is "" (null), then I get an error
> message when I call an OTcl function using the C++ sprintf function  which
> calls the OTcl 'recv' using '%s' for the null field.  
> 
> Maybe the above sounds confusing, here is the code from the C++ side:
> 	sprintf(out, "%s recv %s", name(), hdr->myList);
> And from the OTcl side:
>         Agent/myAgent instproc recv { myList } {
> And the 'send' from the OTcl side:
> 	set thisList ""
> 	lappend thisList "."
> 	$newAgent send $thisNeighbor $thisList

I'm not sure if I understand your question correctly, but:

(a) if you want
to pass arbitrary number of args from otcl to c++ (which is essentially a
list), you know how many args there are by argc in command(), so you can
handle 0/many argument cases conditionally;

(b) if what you are saying is that hdr->myList can be a NULL so
your c++ part will core dump due to incorrect handling in sprintf(), then
can you do a conditional check to see if myList is empty?

(c) if what you said is $thisList is passed to c++ as a single argument,
which can be empty, then perhaps you want to do something like 
$newAgent send $thisNbr [join $thisList] (there is more elegant way to do
this, but join is the most straightforward I can think of now...)
then c++ code will see it as multiple arguments then you can handle it
through argc.

Hope this helps.