How can you print out a tree in a nicely formatted way?

Question

What is the easiest way to print out a tree in it's tree-structure? Such as...

                  some root
              /     |         \
          child1   child2     child 3
           /
      anotherchild               / \
                             yup     another

Even formatting it by hand is hard. How can you make a program print a tree this way?

Answer 1

Unless there is some nice graphical library that you can use, you will have a lot of trouble representing a hierarchy in the way that you describe.

Assuming you want to print it to the Console, or a file, you will have to contend with pre-calculating the lengths of all of the data elements in the entire tree in order to line them up correctly. And how do you handle things like line-wrap?

A much better way is to represent the tree vertically, using indentation to show a child element.

Root
    - Child1
        - Grandchild1
        - Grandchild2
    - Child2
        - Grandchild3
        - Grandchild4

This is much simpler to code, and more tolerant of things like linewrap - as there is only ever one element on a line. This is how a folder-browser or xml document might display its hierarchical data.

To do it this way, you do a depth-first traversal and before the recursive step you print out the node:

public void PrintNode(TreeNode node)
{
    PrintNode(node, 0);
}

private void PrintNode(TreeNode node, int indentation)
{
    // Print the value to the console/file/whatever
    // This prefixes the value with the necessary amount of indentation
    Print(node.Value, indentation);

    // Recursively call the child nodes.
    foreach(TreeNode childNode in node.Children)
    {
        PrintNode(childNode, indentation + 1); // Increment the indentation counter.
    }
}

Hope that helps