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Jan 18, 2021
Jan 18, 2021

tree.hh: an STL-like C++ tree class

by Kasper Peeters <>

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.

What you need

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.

Sample use

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;

   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(two, "peach");

   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;
   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;

The output of this program is:



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.


Projects using tree.hh

The tree.hh library is used in various projects:

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.