iterate through boost property tree

问题

I'm iterating over an XML document using boost property tree and storing the results in a struct. The issue I have is that I can only get to the first "item" nodes and can't access the second "item" nodes. I was hoping someone would point out where I've made a mistake.

My program output looks like this (you can see items are missing.. there is no cookie2, candy2 or chocolate2 items shown):

jar : snAcks
snack : coOkie
item : cooKie1
snack : canDy
item : caNdy1
snack : cHocolate
item : choColate1

Here's the xml file:

<root>
    <jar name="snAcks">
        <snack name="coOkie">
           <item name="cooKie1"></item>
           <item name="cookIe2"></item>
        </snack>
        <snack name="canDy">
           <item name="caNdy1"></item>
           <item name="candY2"></item>
        </snack>
        <snack name="cHocolate">
           <item name="choColate1"></item>
           <item name="chocOlate2"></item>
        </snack>
    </jar>
</root>

Here's the source code:

void parse_xml( boost::property_tree::iptree const& pt )
{
    BOOST_FOREACH( boost::property_tree::iptree::value_type const& v, pt.get_child("root.jar") )
    {
        // Show jar
        if ( boost::iequals( v.first, "<xmlattr>" ) )
        {
            std::cout << "jar : " << v.second.get<std::string>("NaME") << std::endl;
        }

        if ( boost::iequals( v.first, "snack" ) )
        {
            // Show snack
            std::cout << "snack : " << v.second.get<std::string>("<xmlattr>.name")  << std::endl;

            try
            {
                BOOST_FOREACH( boost::property_tree::iptree::value_type const& val, v.second.get_child("item") )
                {
                    if ( boost::iequals( val.first, "<xmlattr>" ) ) {
                        // Show item
                        std::cout << "item : " << val.second.get<std::string>("nAmE")  << std::endl;
                    }
                }
            }

            catch (boost::property_tree::ptree_bad_path& e)
            {
                // Show what caused exception
                std::cout << "Exception: " << e.what() << std::endl;
            }
        }
    }
}

Thank you for taking time to read this. I think I've made a simple mistake, but cannot understand where.

回答1:

I figured it out, but this is not what i would call an intuitive xml-parser library.

void parse_xml( boost::property_tree::iptree const& pt )
{
    BOOST_FOREACH(boost::property_tree::iptree::value_type const& v, pt.get_child("root.jar"))
    {
        // Show jar
        if ( boost::iequals( v.first, "<xmlattr>" ) ) {
            std::cout << "jar : " << v.second.get<std::string>("NaME") << std::endl;
        }

        if ( boost::iequals( v.first, "snack" ) )
        {
            BOOST_FOREACH(boost::property_tree::iptree::value_type const& val, v.second)
            {
                // Show snack
                if ( boost::iequals( val.first, "<xmlattr>" ) ) {
                    std::cout << "snack : " << val.second.get<std::string>("name")  << std::endl;
                }

                if ( boost::iequals(val.first, "item") )
                {
                    BOOST_FOREACH(boost::property_tree::iptree::value_type const& val2, val.second)
                    if ( boost::iequals( val2.first, "<xmlattr>" ) ) {
                        // Show item
                        std::cout << "item : " << val2.second.get<std::string>("nAmE")  << std::endl;
                    }
                }
            }
        }
    }
}

If you compare the two code snippets you can see that mine is bit more regularly structured.

1. Loop over all nodes
2. process the <xmlattr> node
3. process the "real" node.
4. repeat from step 1. inside that node.

来源：https://stackoverflow.com/questions/9216047/iterate-through-boost-property-tree