Starting with version 0.67 of RGP Lua, the tinyxml2 framework is available to Lua scripts in the global namespace tinyxml2.

The original C++ documentation for tinyxml2 is available here:

That documentaion is somewhat sparse. You can get fuller explanations from ChatGPT. A question like, “What is the purpose of the processEntities and whitespaceMode parameters when constructing a tinyxml2.XMLDocument?” yields quite helpful results. (However, the results are not always 100% accurate, so use them with your brain turned on.)

API differences

The Lua implemenation differs from the original documentation as follows:

  • XMLNode::SetUserData is not implemented for Lua. (This is due to memory handling incompatibilities between Lua and C++.)
  • Many of the Set... or Push... functions use C++ overloading that is not available in Lua. For Lua, each numerical setter is named parallel to its getter. Example:


uint64_t x = element->Unsigned64Text() + 1;
element->SetText(x); // uses uint64_t-typed overload of SetText


local x = element:Unsigned64Text() + 1
element:SetUnsigned64Text(x) -- typed name parallel to its getter.
  • The Query... APIs return two values. The first is an error code and the second is the queried value if there is no error. This second returned value eliminates the need for the final pointer paremeters in the C++ versions.


double x = 0;
tinyxml2::XMLError result = element->QueryDoubleAttribute("percent", &x) // 2 parameters


local result, x = element:QueryDoubleAttribute("percent") -- 1 parameter
  • Each of the classes has a ClassName method added that is not in the original documentation.
  • XMLPrinter is available for memory buffer printing only. If you need to write to a file, use io.write to write the CStr of the XMLPrinter to the file.
  • XMLDocument defines XMLDocument::Clear as a close function with Lua 5.4+. That means you can use the Lua 5.4 <close> keyword to specify that the document is cleared immediately on any exit path from the block in which it is defined.
local xml <close> = tinyxml2.XMLDocument()
  • Similarly XMLPrinter defines XMLPrinter::ClearBuffer as a close function with Lua 5.4.
local xml_printer <close> = tinyxml2.XMLPrinter()
  • The Lua constructors for XMLDocument and XMLPrinter accept a variable number of parameters with default values the same as documented for C++.


tinyxml2::XMLDocument doc_with_defaults;
tinyxml2::XMLDocument doc_with_settings(false, tinyxml2::COLLAPSE_WHITESPACE);


local doc_with_defaults = tinyxml2.XMLDocument()
local doc_with_settings = tinyxml2.XMLDocument(false, tinyxml2.COLLAPSE_WHITESPACE)

The latest version of the RGP Lua Class Browser provides a working example of a script that uses tinyxml2.

Built-in functions for XML

When RGP Lua loads the tinyxml2 library, it also loads the following built-in functions to facilitate iterating xml documents.

xmlelements(node [, nodename])

xmlelements() feeds a for loop with child elements of a node in order. It feeds only elements that are direct descendants of the node and does not recurse. If the optional nodename string is supplied, it iterates only on nodes with that name.


local xml = tinyxml2.XMLDocument()
for element in xmlelements(xml) do
   print ("Name: ", element:Name(), "Text: ", tostring(element:GetText()))


xmlattributes() feeds a for loop with the attributes of an XMLElement. If the node passed in is not convertible to an XMLElement instance, it does nothing.


local xml = tinyxml2.XMLDocument()
for element in xmlelements(xml:FirstChildElement()) do
    for attr in xmlattributes(element) do
       print ("Name: ", attr:Name(), "Text: ", attr:Value())