This example shows how to generate a JSON document with ArduinoJson.

Source code

// ArduinoJson -
// Copyright Benoit Blanchon 2014-2018
// MIT License

#include <ArduinoJson.h>

void setup() {
  // Initialize Serial port
  while (!Serial) continue;

  // Memory pool for JSON object tree.
  // Inside the brackets, 200 is the size of the pool in bytes.
  // Don't forget to change this value to match your JSON document.
  // Use to compute the capacity.
  StaticJsonBuffer<200> jsonBuffer;

  // StaticJsonBuffer allocates memory on the stack, it can be
  // replaced by DynamicJsonBuffer which allocates in the heap.
  // DynamicJsonBuffer  jsonBuffer(200);

  // Create the root of the object tree.
  // It's a reference to the JsonObject, the actual bytes are inside the
  // JsonBuffer with all the other nodes of the object tree.
  // Memory is freed when jsonBuffer goes out of scope.
  JsonObject& root = jsonBuffer.createObject();

  // Add values in the object
  // Most of the time, you can rely on the implicit casts.
  // In other case, you can do root.set<long>("time", 1351824120);
  root["sensor"] = "gps";
  root["time"] = 1351824120;

  // Add a nested array.
  // It's also possible to create the array separately and add it to the
  // JsonObject but it's less efficient.
  JsonArray& data = root.createNestedArray("data");

  // This prints:
  // {"sensor":"gps","time":1351824120,"data":[48.756080,2.302038]}


  // This prints:
  // {
  //   "sensor": "gps",
  //   "time": 1351824120,
  //   "data": [
  //     48.756080,
  //     2.302038
  //   ]
  // }

void loop() {
  // not used in this example

Classes used in this example

Functions used in this example

Keep learning

Mastering ArduinoJson

The chapter “Serialize with ArduinoJson” of Mastering ArduinoJson is a tutorial to learn how to generate JSON documents with the library. It begins with a simple example, like the one above, and then adds more features like serializing directly to a file or an HTTP request.