[ns] segmentation fault while calling getLoc function(getting node position)

[Ghofrane]

Hello,
I
need to get the current position of the node during the simulation,
so I added in the cc file:
double ox,oy,oz;
MobileNode *
otherNode;
otherNode = (MobileNode
*)(Node::get_node_by_address(id));
otherNode->getLoc(&ox,&oy,&oz);

but
I have a segmentation fault at the beginning of the simulation. Can you help me 
please to   solve this problem ?
Is there any other method to know  the current node position?

Thanks