c++xmlboostboost-propertytree

Accessing multi-valued keys in Property Tree


I am trying to query multi-valued keys in Property Tree.

I have taken the reference from this SO link.

Here is a piece of my Xml:

<Element type="MyType">
<Name type="Number">
<KeyFrame time="0">1920</KeyFrame>
<KeyFrame time="3000">1080</KeyFrame>
<KeyFrame time="4000">720</KeyFrame>
</Name>
</Element>

Following is the code :

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
#include <sstream>
#include <iostream>

using boost::property_tree::ptree;

int main() {
    std::stringstream ss("<Element type=\"MyType\">" 
    "<Name type=\"Number\">"
    "<KeyFrame time=\"0\">1920</KeyFrame>"
    "<KeyFrame time=\"3000\">1080</KeyFrame>" 
    "<KeyFrame time=\"4000\">720</KeyFrame></Name>" 
    "</Element>");

    ptree pt;
    boost::property_tree::read_xml(ss, pt);
   
    auto& root =  pt.get_child("Element");
    for (auto& child : root.get_child("Name"))
    {
        if(child.first == "KeyFrame")
        {
            std::cout<<child.second.get<int>("<xmlattr>.time", 0)<<" : "<<child.second.data()<<std::endl;
        }
    }
 }

Here I am able to access the <xmlattr>.time by specifying the type int but the value is retrieved in a string using child.second.data().

Can I specify the type for value as well? something like child.second.get<int>, So that I get the value in its type for ex int, double etc. and not as a string.


Solution

  • I'd suggest get_value<>:

    Live On Coliru

    #include <boost/property_tree/ptree.hpp>
    #include <boost/property_tree/xml_parser.hpp>
    #include <iostream>
    #include <sstream>
    
    std::string const sample = R"(<Element type="MyType">
        <Name type="Number">
            <KeyFrame time="0">1920</KeyFrame>
            <KeyFrame time="3000">1080</KeyFrame>
            <KeyFrame time="4000">720</KeyFrame>
        </Name>
    </Element>)";
    
    using boost::property_tree::ptree;
    
    int main() {
      std::stringstream ss(sample);
    
      ptree pt;
      boost::property_tree::read_xml(ss, pt);
    
      auto &root = pt.get_child("Element");
      for (auto &child : root.get_child("Name")) {
        if (child.first == "KeyFrame") {
            auto node = child.second;
            std::cout << node.get<int>("<xmlattr>.time", 0) << " : "
                      << node.get_value<int>() << std::endl;
        }
      }
    }
    

    Prints

    0 : 1920
    3000 : 1080
    4000 : 720