Boost 1.46.1, Property Tree: How to iterate through ptree receiving sub ptrees?

Question

First of all I shall say that I think I got how it should be done but my code will not compile any way I try. I based my assumption on this official example of empty ptree t

Answer 1

The property tree iterators point to pairs of the form (key, tree) of type ptree::value_type. The standard loop for iterating through the children of the node at path therefore looks like:

BOOST_FOREACH(const ptree::value_type &v, pt.get_child(path)) {
    // v.first is the name of the child.
    // v.second is the child tree.
}

Answer 2

I had the same problem with iterating trough JSON sub nodes

boost::property_tree::read_json(streamJSON, ptJSON);

If you have a structure like:

{
 playlists: [ {
   id: "1",
   x: "something"
   shows: [
    { val: "test" },
    { val: "test1" },
    { val: "test2" }
   ]
 },
 {
   id: "2"
   x: "else",
   shows: [
    { val: "test3" }
   ]
 }
 ]
}

You can iterate trough child nodes like this:

BOOST_FOREACH(boost::property_tree::ptree::value_type &playlist, ptJSON.get_child("playlists"))
{
    unsigned long uiPlaylistId = playlist.second.get<unsigned long>("id");
    BOOST_FOREACH(boost::property_tree::ptree::value_type &show, playlist.second.get_child("shows."))
    {
       std::string strVal = show.second.get<std::string>("val");
    }
}

I could not find anything about path selector "shows." to select sub array. (notice the dot at the end)

Some good documentation can be found here: http://kaalus.atspace.com/ptree/doc/index.html

Hope this helps someone.

Answer 3

Using C++11, you can use the following to iterate through all the children of the node at path:

ptree children = pt.get_child(path);
for (const auto& kv : children) {
    // kv is of type ptree::value_type
    // kv.first is the name of the child
    // kv.second is the child tree
}