Arduino JSON v4 was a major rewrite of the library, and the API change significantly.
## Includes
Arduino JSON v3 had two include files:
#include<JsonParser.h>
#include<JsonGenerator.h>
Arduino JSON v4 only has one:
#include<ArduinoJson.h>
Node: the header `src/ArduinoJson.h` is intended to be used within the Arduino IDE, if you're in another environment, you may need to include the following headers:
#include<ArduinoJson/StaticJsonBuffer.hpp>
#include<ArduinoJson/JsonObject.hpp>
#include<ArduinoJson/JsonArray.hpp>
## Namespaces
Arduino JSON v3 had two namespaces:
using namespace ArduinoJson::Parser;
using namespace ArduinoJson::Generator;
Arduino JSON v4 only has one:
using namespace ArduinoJson;
If you include the header `ArduinoJson.h` (recommended if in Arduino IDE), the `using` directivei is already done for you, so you don't have to write it.
## StaticJsonBuffer
Arduino JSON v3 had different memory allocation models for parser:
JsonParser<16> parser; // 16 being the capacity in "tokens"
and for the generator:
JsonArray<4> array; // 4 being the number of element
JsonObject<4> object;
Arduino JSON v4 only has one memory allocation mode:
StaticJsonBuffer<128> buffer; // 128 being the capacity in bytes
## Return values for the parser
Arduino JSON v3 returned `JsonArray` and `JsonObject`:
JsonArray array = parser.parseArray(json);
JsonObject object = parser.parseObject(json);
Arduino JSON v4 returns references:
JsonArray& array = buffer.parseArray(json);
JsonObject& object = buffer.parseObject(json);
Everything else is compatible
## Creating arrays and objects
Arduino JSON v3 allowed to create `JsonArray` and `JsonObject` directly:
JsonArray<4> array;
JsonObject<4> object;
Arduino JSON v4 requires that you use a `StaticJsonBuffer` for that:
JsonArray& array = buffer.createArray();
JsonObject& object = buffer.createObject();
Note: you don't have to specify the capacity anymore.
## Printable interface
Arduino JSON v3 used to implement the Printable interface, that allowed that kind of statement:
Serial.print(array);
Arduino JSON v4 doesn't, so you need to write this:
array.printTo(Serial);
Note: there is a good reason for that: reducing the size of `JsonArray` and `JsonObject`.
