by Kasper Peeters <kasper.peeters@phi-sci.com>

The tree.hh library for C++ provides an STL-like container class for n-ary trees, templated over the data stored at the nodes. Various types of iterators are provided (post-order, pre-order, and others). Where possible the access methods are compatible with the STL or alternative algorithms are available.

The library should work with any C++11 compiler, and has been used and tested on all major platforms (Linux, Windows, macOS, Android, iOS).

The library is available under the terms of the GNU General Public License version 2 or 3.

The tree.hh is header-only; you only need to copy the src/tree.hh header file into your project and you are good to go.

Then scan the example below and consult the documentation.

The following is a small sample program to illustrate how tree.hh is used:

#include <algorithm>
#include <string>
#include <iostream>
#include "tree.hh"

using namespace std;

int main(int, char **)
   {
   tree<string> tr;
   tree<string>::iterator top, one, two, loc, banana;

   top=tr.begin();
   one=tr.insert(top, "one");
   two=tr.append_child(one, "two");
   tr.append_child(two, "apple");
   banana=tr.append_child(two, "banana");
   tr.append_child(banana,"cherry");
   tr.append_child(two, "peach");
   tr.append_child(one,"three");

   loc=find(tr.begin(), tr.end(), "two");
   if(loc!=tr.end()) {
   tree<string>::sibling_iterator sib=tr.begin(loc);
   while(sib!=tr.end(loc)) {
     cout << (*sib) << endl;
     ++sib;
     }
   cout << endl;
   tree<string>::iterator sib2=tr.begin(loc);
   tree<string>::iterator end2=tr.end(loc);
   while(sib2!=end2) {
     for(int i=0; i<tr.depth(sib2)-2; ++i) 
        cout << " ";
     cout << (*sib2) << endl;
     ++sib2;
     }
   }
}

The output of this program is:

apple
banana
peach

apple
banana
 cherry
peach

Note that this example only has one element at the top of the tree (in this case that is the node containing one) but it is possible to have an arbitary number of such elements (then the tree is more like a "bush"). Observe the way in which the two types of iterators work. The first block of output, obtained using the sibling_iterator, only displays the children directly below two. The second block iterates over all children at any depth below two. In the second output block, the depth member has been used to determine the distance of a given node to the root of the tree.

The tree.hh library is used in various projects:

• Cadabra (https://cadabra.science/), a field-theory motivated approach to symbolic computer algebra.
• Taxator-tk (https://github.com/fungs/taxator-tk/), a set of programs for the taxonomic analysis of nucleotide sequence data.
• Gnash (http://www.gnu.org/software/gnash/), a GNU Flash movie player. Previously, it was only possible to play flash movies with proprietary software. While there are some other free flash players, none support anything beyond SWF v4. Gnash is based on GameSWF, and supports many SWF v7 features.
• htmlcxx (http://htmlcxx.sourceforge.net/), a simple non-validating css1 and html parser for C++.
• Principles of Compiler Design (http://www.cs.sfu.ca/~anoop/courses/CMPT-379-Fall-2007/index.html), a course in compiler design at the Simon Fraser University, Canada.
• liborigin (http://sourceforge.net/projects/liborigin/), a library for reading OriginLab OPJ project files, which is used by QtiPlot (http://soft.proindependent.com/qtiplot.html) and LabPlot (http://labplot.sourceforge.net/), two applications for data analysis and visualisation.
• EChem++ (http://www.echem.uni-tuebingen.de/~bs/echem/software/EChem++/echem++.shtml), a project realizing the idea of a Problem Solving Environment (PSE) in the field of computational electrochemistry. Computer controlled experimental measurements, numerical simulation and analysis of electrochemical processes will be combined under a common user interface.
• LZCS (http://www.infor.uva.es/~jadiego/), a semistructured document transformation tool. LZCS compresses structured documents taking advantage of the redundant information that can appear in the structure. The main idea is that frequently repeated subtrees may exist and these can be replaced by a backward reference to their first occurance. See the paper (http://www.dcc.uchile.cl/~gnavarro/ps/dcc04.1.ps.gz).
• libOFX (http://libofx.sourceforge.net/), a parser and an API designed to allow applications to very easily support OFX command responses, usually provided by financial institutions for statement downloads.
• A genetic programming project (http://www.cs.adfa.edu.au/~shanyin/publications/peel.pdf).
• FreeLing (http://nlp.lsi.upc.edu/freeling/) a library providing language analysis services (such as morfological analysis, date recognition, PoS tagging, and so on.

Let me know about your project when you are using tree.hh, so that I can add it to the list.

In principle, the tree.hh code is available under the terms of the GNU General Public License 2 or 3. However, if you would like to use tree.hh under different conditions, contact me and we will work something out.