Inputting a Tree from Disk

If someone has written a file containing FARFALLA trees to disk, you may read those trees in by calling F_inputTree(), F_inputTree() provided that you know the type of the top-level node in the tree. (If not, you will have to use the more complicated F_inputSubtree() routine, discussed in the reference section, Section .) F_inputTree() takes two arguments. The first is a pointer to a node of the proper type. The second is a file (actually an iostream) from which to read. The file must be previously opened. F_inputTree() reads exactly one entire tree from disk and makes the pointer point at the top node of the tree. As before, when you are finished using a tree you must delete it to free up the memory it was occupying.

The following program might be the generic shell for analysis programs. It reads every event from a file of event trees and if the run number passes a cut, calls user analysis routines. The analysis routines receive a pointer to the top of the tree from the main routine. (Usually we use a global variable rather than a subroutine parameter to pass the pointer.) After analysis the tree is deleted. The program continues until the input file is exhausted; at that time F_inputTree returns NULL.

fstream infile;
infile.open("locfile.far",ios::in);

eventNode *evPtr;
F_inputTree(evPtr,infile);      // this creates the tree in memory and
                                // makes evPtr point at its top node

while (evPtr != NULL)           // F_inputTree() will make evPtr NULL
                                // when the input file has been exhausted
{
  if (evPtr->run > 1000) do_user_analysis(evPtr);
  evPtr->deleteSubtree();       // free up the memory
  F_inputTree(evPtr,infile);    // get the next tree into memory
}