Parsing JSON on the Arduino

Question

I'm using the ArduinoJson library. There is a great example for parsing a single JSON object in the source code. I am attempting to iterate over an array of JSON objects:

#include <JsonParser.h>

using namespace ArduinoJson::Parser;

void setup() {
  Serial.begin(9600);

  char json[] = "[{\"sensor\":\"gps\",\"time\":1351824120,\"data\":[48.756080,2.302038]}, \
    {\"sensor\":\"gps\",\"time\":1351824140,\"data\":[50.756080,21.302038]}]";

  JsonParser<32> parser;
  JsonArray root = parser.parse(json);

  if (!root.success()) {
    Serial.println("JsonParser.parse() failed");
    return;
  }

  for (JsonArrayIterator item = root.begin(); item != root.end(); ++item) {
    // unsure of what to do here.

    Serial.println((*item)["data"]);
    // results in: 
    // ParseJsonArray:21: error: call of overloaded 
    //   'println(ArduinoJson::Parser::JsonValue)' is ambiguous

    JsonObject something = JsonObject(*item);
    Serial.println(something["sensor"]);
    // results in :
    // ParseJsonArray:26: error: call of overloaded
    //   'println(ArduinoJson::Parser::JsonValue)' is ambiguous
  }
}

void loop() {}

item is of type JsonValue. I would like to treat it as a JsonObject and pull some data out of it.

Answer 1

This is how I would write this loop:

for (JsonArrayIterator it = root.begin(); it != root.end(); ++it) 
{    
  JsonObject row = *it;    

  char*  sensor    = row["sensor"];  
  long   time      = row["time"];  
  double latitude  = row["data"][0];
  double longitude = row["data"][1];

  Serial.println(sensor);
  Serial.println(time);
  Serial.println(latitude, 6);
  Serial.println(longitude, 6);
}

And, if C++11 is available (which is not the case with Arduino IDE 1.0.5):

for (auto row : root) 
{    
  char*  sensor    = row["sensor"];  
  long   time      = row["time"];  
  double latitude  = row["data"][0];
  double longitude = row["data"][1];

  Serial.println(sensor);
  Serial.println(time);
  Serial.println(latitude, 6);
  Serial.println(longitude, 6);
}

Answer 2

Got it! Initially, casting the retrieval of the item from the JsonObject before printing was enough.

JsonObject something = JsonObject(*item);
Serial.println((char*)something["sensor"]);

Although, I think this looks better.

char* sensor = (*item)["sensor"];
Serial.println(sensor);