[ns] Creating new variable in c++ & accessing via TCL??

["Susan Tsao" <SusanTsao@WoodsideNet.Com>]

Hello,

I created a new variable in mac-802_11.*  file, which I like to access
via 
my TCL script. However, it doesn't work. Can someone please tell me 
what I did wrong?  
------------------------------------------------------------------------
---------------------------------

I created a variable called 'collision_count' which counts the number of

mac-802_11 collisions.  And I like to access this value at the end of my
simulation. 

3 steps:

1) Added following line to mac-802_11.h:

	class Mac802_11 : public Mac {   
		private:
			int  collision_count;      	// added a
private data memeber
	};       


2) Changes to mac-802_11.cc:
	a) Initialize collison_count =0 in the constructor
Mac802_11::Mac802_11( )
	b) Increment "collision_count"  as follows

	Mac802_11::collision(Packet *p)  {

   	   if(TX_Time(p) > mhRecv_.expire()) {
                        mhRecv_.stop();
                        discard(pktRx_, DROP_MAC_COLLISION);
		collision_count+=1;			// **** i  added
this line 
                        pktRx_ = p;
                        mhRecv_.start(TX_Time(pktRx_));
                }
                else {
                        discard(p, DROP_MAC_COLLISION);
		collision_count +=1;			// **** i added
this line
                } 

3) My simulations consists of several wireless node sending packets to a
base station.
    And I want to access "colllision_count" at the end of my
simulations, so I have following
    in my TCL script.

set macobject [new Mac/802_11]
$ns_ at $simulation_endtime "count"

proc count {} {
        global macobject 
        set colcount [$macobject set collision_count]
        puts "$count"
}
    
4) run my scripts, but it outputs errors:

ns: count: can't read "collision_count": no such variable
    while executing
"subst $[subst $var]"
    (procedure "_o156" line 5)
    (SplitObject set line 5)
    invoked from within
"$macobject set collision_count"
    (procedure "count" line 3)
    invoked from within
"count"


Has anyone done something similar to other classes? 
Any help is appreciated!

Thanks.

susan