This routine reads one tree off of disk (from the file described by
the iostream variable infile) and makes topNodePtr
point at the top node of the tree. The tree must have been written by
the outputSubtree() command documented below in
Section 
. topNodePtr must be a pointer to the
proper type of node; i.e. the type of the top node in the tree that
is going to be read. If you do not know the type, you must use the
more general F_inputSubtree() function documented in the next
section.
The following reads one event tree from a file.
fstream infile; // declare the fstream variable
infile.open("infile.dst",ios::in);
eventNode *ev;
F_inputTree(ev,infile); // ev points at the top of a new tree
if (ev->run > 1000) ...
Note that you may pass an fstream instead of an iostream as the second argument to F_inputTree().