Cookbooks
Arduino
Chapter 10. Data Formats and Serialization
Working with XML

Arduino:
Working with XML

How to:

We’ll use the XMLWriter library to create XML and the tinyxml2 library to parse it. Install the libraries first via the Library Manager in your Arduino IDE.

Creating an XML document:

#include <XMLWriter.h>

void setup() {
  Serial.begin(9600);
  
  XMLWriter xml(&Serial); // Using Serial to output
  
  xml.header();
  xml.tag("greeting").tag("text").text("Hello, world!").close().close();
  xml.flush();
}

void loop() {
}

Decoding an XML string:

#include <tinyxml2.h>

tinyxml2::XMLDocument doc;
doc.Parse("<greeting><text>Hello, world!</text></greeting>");

tinyxml2::XMLElement* text = doc.FirstChildElement("greeting")->FirstChildElement("text");
if (text != nullptr) {
  Serial.println(text->GetText());
}

Sample output:

<greeting>
  <text>Hello, world!</text>
</greeting>

Deep Dive

XML, or Extensible Markup Language, is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. It’s been around since the late ’90s and is used extensively in various fields, especially where platform-independent data exchange is needed. Arduino’s limited memory resources make working with XML more challenging than on a PC. Hence, lightweight libraries are crucial. Although JSON has gained popularity for data exchange due to its simpler syntax and smaller footprint, XML is still used widely, especially when dealing with legacy systems or applications that require document validation via schemas. Key to Arduino XML implementation is stream parsing, which reads the document in segments to keep memory usage low.

See Also

Working with JSONWorking with YAML