boost_1_45_0/libs/property_tree/examples/debug_settings.cpp

// ----------------------------------------------------------------------------
// Copyright (C) 2002-2006 Marcin Kalicinski
//
// Distributed under the Boost Software License, Version 1.0. 
// (See accompanying file LICENSE_1_0.txt or copy at 
// http://www.boost.org/LICENSE_1_0.txt)
//
// For more information, see www.boost.org
// ----------------------------------------------------------------------------

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
#include <boost/foreach.hpp>
#include <string>
#include <set>
#include <exception>
#include <iostream>

struct debug_settings
{
    std::string m_file;               // log filename
    int m_level;                      // debug level
    std::set<std::string> m_modules;  // modules where logging is enabled
    void load(const std::string &filename);
    void save(const std::string &filename);
};

void debug_settings::load(const std::string &filename)
{

    // Create empty property tree object
    using boost::property_tree::ptree;
    ptree pt;

    // Load XML file and put its contents in property tree. 
    // No namespace qualification is needed, because of Koenig 
    // lookup on the second argument. If reading fails, exception
    // is thrown.
    read_xml(filename, pt);

    // Get filename and store it in m_file variable. Note that 
    // we specify a path to the value using notation where keys 
    // are separated with dots (different separator may be used 
    // if keys themselves contain dots). If debug.filename key is 
    // not found, exception is thrown.
    m_file = pt.get<std::string>("debug.filename");
    
    // Get debug level and store it in m_level variable. This is 
    // another version of get method: if debug.level key is not 
    // found, it will return default value (specified by second 
    // parameter) instead of throwing. Type of the value extracted 
    // is determined by type of second parameter, so we can simply 
    // write get(...) instead of get<int>(...).
    m_level = pt.get("debug.level", 0);

    // Iterate over debug.modules section and store all found 
    // modules in m_modules set. get_child() function returns a 
    // reference to child at specified path; if there is no such 
    // child, it throws. Property tree iterator can be used in 
    // the same way as standard container iterator. Category 
    // is bidirectional_iterator.
    //BOOST_FOREACH(ptree::value_type &v, pt.get_child("debug.modules"))
    //    m_modules.insert(v.second.data());

}

void debug_settings::save(const std::string &filename)
{

    // Create empty property tree object
    using boost::property_tree::ptree;
    ptree pt;

    // Put log filename in property tree
    pt.put("debug.filename", m_file);

    // Put debug level in property tree
    pt.put("debug.level", m_level);

    // Iterate over modules in set and put them in property
    // tree. Note that the add function places new key at the
    // end of list of keys. This is fine in most of the
    // situations. If you want to place item at some other
    // place (i.e. at front or somewhere in the middle),
    // this can be achieved using a combination of the insert
    // and put_value functions
    BOOST_FOREACH(const std::string &name, m_modules)
        pt.add("debug.modules.module", name);
    
    // Write property tree to XML file
    write_xml(filename, pt);

}

int main()
{
    try
    {
        debug_settings ds;
        ds.load("debug_settings.xml");
        ds.save("debug_settings_out.xml");
        std::cout << "Success\n";
    }
    catch (std::exception &e)
    {
        std::cout << "Error: " << e.what() << "\n";
    }
    return 0;
}