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 trick. There you can find next line:

  const ptree &settings = pt.get_child("settings", empty_ptree<ptree>());

Which shows that it is (or should be) possible to get subptree out from ptree.

So I assumed we could iterate thru ptree with something like BOOST_FOREACH in such manner:

BOOST_FOREACH(const boost::property_tree::ptree &v,
    config.get_child("servecies"))
{

}

But I get next error:

Error 1 error C2440: 'initializing' : cannot convert from 'std::pair<_Ty1,_Ty2>' to 'const boost::property_tree::ptree &'

or if I try

BOOST_FOREACH(boost::property_tree::ptree &v,
    config.get_child("servecies", boost::property_tree::empty_ptree<boost::property_tree::ptree>()))
{

}

I get:

Error 1 error C2039: 'empty_ptree' : is not a member of 'boost::property_tree'

So what shall I do: how to iterate thru Boost Ptree and get sub Ptrees?

Update: I also tried such code

    BOOST_FOREACH(boost::property_tree::ptree::value_type &v,
    config.get_child("path.to.array_of_objects"))
{
    std::cout << "First data: " << v.first.data() << std::endl;
    boost::property_tree::ptree subtree = (boost::property_tree::ptree) v.second ;
    BOOST_FOREACH(boost::property_tree::ptree::value_type &vs,
        subtree)
    {
        std::cout << "Sub data: " << vs.first.data() << std::endl;
    }
}

This compiles, does not throw any exeptions but does not cout any Sub data, it just skeeps thru this cycle.

Update 2:

Hm... something probably went wrong in my xml - now I get correct results with that code.

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.
}