boost::property_tree::xml_parser and json_parser are hardcoded to work only with keys of std::string type. The following code will fail to compile: boost::property_tree::basic_ptree pt; std::string filename("123.xml"); boost::property_tree:xml_parser::read_xml(filename, pt); I have prepared a patch that removes this limitation. Please consider pulling https://github.com/sanderbog/property_tree/commit/8af8b6bf3b65fa59792d849b52... Kind Regards, Alexander Bogdashevsky