An HTTP server sends me a JSON response (a string) like this :
{ \"folders\" : [{ \"id\" : 109, \"parent_id\" : 110,
Use Boost's built-in json parser to property tree:
http://www.boost.org/doc/libs/1_57_0/doc/html/boost_propertytree/parsers.html#boost_propertytree.parsers.json_parser