enum input from xml to c++ program using boost::property_tree

Question

How do you read a enum-class from an XML file using the boost::property_tree library?

I would like to avoid reading it as a string and mapping the string to the enum-class in my program.

Answer 1

Read the property_tree/xml_parser.hpp header file. It's pretty straightforward.

Here are the most important parts, all in the boost::property_tree::xml_parser namespace:

/**
     * Reads XML from an input stream and translates it to property tree.
     * @note Clears existing contents of property tree.  In case of error the
     *       property tree unmodified.
     * @note XML attributes are placed under keys named @c \<xmlattr\>.
     * @throw xml_parser_error In case of error deserializing the property tree.
     * @param stream Stream from which to read in the property tree.
     * @param[out] pt The property tree to populate.
     * @param flags Flags controlling the behaviour of the parser.
     *              The following flags are supported:
     * @li @c no_concat_text -- Prevents concatenation of text nodes into
     *                          datastring of property tree.  Puts them in
     *                          separate @c \<xmltext\> strings instead.
     * @li @c no_comments -- Skip XML comments.
     * @li @c trim_whitespace -- Trim leading and trailing whitespace from text,
     *                           and collapse sequences of whitespace.
     */
    template<class Ptree>
    void read_xml(std::basic_istream<
                      typename Ptree::key_type::value_type
                  > &stream,
                  Ptree &pt,
                  int flags = 0)
    {
        read_xml_internal(stream, pt, flags, std::string());
    }

    /**
     * Reads XML from a file using the given locale and translates it to
     * property tree.
     * @note Clears existing contents of property tree.  In case of error the
     *       property tree unmodified.
     * @note XML attributes are placed under keys named @c \<xmlattr\>.
     * @throw xml_parser_error In case of error deserializing the property tree.
     * @param filename The file from which to read in the property tree.
     * @param[out] pt The property tree to populate.
     * @param flags Flags controlling the bahviour of the parser.
     *              The following flags are supported:
     * @li @c no_concat_text -- Prevents concatenation of text nodes into
     *                          datastring of property tree.  Puts them in
     *                          separate @c \<xmltext\> strings instead.
     * @li @c no_comments -- Skip XML comments.
     * @param loc The locale to use when reading in the file contents.
     */
    template<class Ptree>
    void read_xml(const std::string &filename,
                  Ptree &pt,
                  int flags = 0,
                  const std::locale &loc = std::locale())
    {
        BOOST_ASSERT(validate_flags(flags));
        std::basic_ifstream<typename Ptree::key_type::value_type>
            stream(filename.c_str());
        if (!stream)
            BOOST_PROPERTY_TREE_THROW(xml_parser_error(
                "cannot open file", filename, 0));
        stream.imbue(loc);
        read_xml_internal(stream, pt, flags, filename);
    }