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.

• user13842: does the data parse from above object is for both sensor how to parse value of each object of jason LIKE i have [{"sensor":"gps", "time":"1351824120"},{"sensor":"temp", "time":"1351824120"}]

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);