current community

your communities

more stack exchange communities

Stack Exchange
tour help
Take the 2-minute tour ×
Arduino Stack Exchange is a question and answer site for developers of open-source hardware and software that is compatible with Arduino. It's 100% free, no registration required.
up vote 3 down vote favorite
1

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.

share|improve this question

2 Answers 2

up vote 1 down vote accepted

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);
}
share|improve this answer
up vote 1 down vote

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);
share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.