ARDUINOJSON_ENABLE_ARDUINO_STRING

Enables support of the type String in the library.

The default is 1 of ARDUINO is defined, 0 otherwise. In other words, String is supported as soon as you work in an Arduino-compatible environment

How to force the value?

If you need to force the support of String, add this at the top of your program:

#define ARDUINOJSON_ENABLE_ARDUINO_STRING 1
#include <ArduinoJson.h>

On the other hand, if you need to disable String, do:

#define ARDUINOJSON_ENABLE_ARDUINO_STRING 0
#include <ArduinoJson.h>

Where a String can be used?

Once enabled, you can use a String in many places.

  1. You can use a String as your JSON input

     // WARNING: the content of the String will be duplicated in the JsonBuffer.
 String input = "{\"sensor\":\"gps\",\"time\":1351824120,\"data\":[48.756080,2.302038]}";
 JsonObject& root = jsonBuffer.parseObject(input);

  2. You can use a String to get an element of a JsonObject

     long time = root[String("time")];

  3. You can use a String to set an element of a JsonObject

     // WARNING: the content of the String will be duplicated in the JsonBuffer.
 root[String("time")] = time;

  4. You can get a String from a JsonObject or JsonArray

     String sensor = root["sensor"];

  5. You can set a String to a JsonObject or JsonArray:

     // WARNING: the content of the String will be duplicated in the JsonBuffer.
 root["sensor"] = sensor;

  6. You can also concatenate strings

     // WARNING: the content of the String will be duplicated in the JsonBuffer.
 root[String("sen") + "sor"] = String("gp") + "s";

  7. You can compare the content of a JsonObject with a String

     if (root["sensor"] == sensor) {
     // ...
 }

  8. You can print the resulting JSON to a String

     String output;
 root.printTo(output);

Where a String can not be used?

  1. Unfortunately, the following doesn’t work (issue #118):

     String sensor = "something";
 sensor = root["sensor"]; // <-  error "ambiguous overload for 'operator='"

  2. As a workaround, you need to replace by:

     sensor = root["sensor"].as<String>();

See also