Compare std::vector of pairs with pugi::xml_object_range attributes - c++

Question

I'm writing some convenience functions for my XML parser based on pugixml, and now I have the problem that I want to retrieve only XML nodes with a specific attribute name and value!
XML example:
<Readers>
<Reader measurement="..." type="Mighty">
<IP reader="1">192.168.1.10</IP>
<IP reader="2">192.168.1.25</IP>
<IP reader="3">192.168.1.30</IP>
<IP reader="4">192.168.1.50</IP>
</Reader>
<Reader measurement="..." type="Standard">
...
</Reader>
</Readers>
My try:
std::string GetNodeValue(std::string node, std::vector<std::pair<std::string,std::string>> &attributes)
{
pugi::xml_node xmlNode = m_xmlDoc.select_single_node(("//" + node).c_str()).node();
// get all attributes
pugi::xml_object_range<pugi::xml_attribute_iterator> nodeAttributes(xmlNode.attributes());
// logic to compare given attribute name:value pairs with parsed ones
// ...
}
Can someone help me or give me a hint?! (maybe with Lambda Expressions)

Answer 1

To solve this we have to use XPath.
/*!
Create XPath from node name and attributes
#param XML node name
#param vector of attribute name:value pairs
#return XPath string
*/
std::string XmlParser::CreateXPath(std::string node, std::vector<std::pair<std::string,std::string>> &attributes)
{
try
{
// create XPath
std::string xpath = node + "[";
for(auto it=attributes.begin(); it!=attributes.end(); it++)
xpath += "#" + it->first + "='" + it->second + "' and ";
xpath.replace(xpath.length()-5, 5, "]");
return xpath;
}
catch(std::exception exp)
{
return "";
}
}
CreateXPath constructs a valid XML XPath statement from given node name and attribute list.
/*!
Return requested XmlNode value
#param name of the XmlNode
#param filter by given attribute(s) -> name:value
#return value of XmlNode or empty string in case of error
*/
std::string XmlParser::GetNodeValue(std::string node, std::vector<std::pair<std::string,std::string>> &attributes /* = std::vector<std::pair<std::string,std::string>>() */)
{
try
{
std::string nodeValue = "";
if(attributes.size() != 0) nodeValue = m_xmlDoc.select_node(CreateXPath(node, attributes).c_str()).node().child_value();
else nodeValue = m_xmlDoc.select_node(("//" + node).c_str()).node().child_value();
return nodeValue;
}
catch(std::exception exp)
{
return "";
}
}