Question about JSON

Projects Programming
1

Hello to all the Arduino community,

I am a French student in the last year of high school and I have to realize a project that displays the next train times. So, I decided to use an Arduino (ESP-8266) and an I2c screen.

For the moment, I want to get from a website data in JSON (with an API, it works).
But, when I want for example to get the train name it doesn't work all the time, it depends on the syntax of JSON.

Here is an illustration of my problem:

First example :

There are only "{" and "}" at the beginning and the end of the file. It works with my code.

Capture 1

Second example : There are "[" and "]" at the beginning and the end of the json file, there are still the "{" and "}". I want to get the "shortName", "vehicleName"... But it does not work...

Capture 2

Here is my code to grab the information from the website, it only works with the first example :

      int id = root["id"]; 
      const char* shortName = root["shortName"]; 
      const char* vehicleName = root["vehicleName"]; 
      const char* lineDirection = root["lineDirection"]; 
      const char* time = root["time"];

So, does anyone know how to edit the code in order that it will work with the "[", "{", "}" "]" ?

Thank you very much for reading my and for your answers !
Lucas

2

What programming language is your code snippet written in ?

3

My snippet is probably the arduino programming language which should be "C".

Here is the full code if you want :

#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <ArduinoJson.h>


const char* ssid = "XX";
const char* password = "XX";

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);
 
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting...");
  }
}

void loop() {

  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;  
    http.begin("http://perfeito.fr/test.json");
    int httpCode = http.GET();
                                                                
    if (httpCode > 0) {
   
      const size_t bufferSize = JSON_OBJECT_SIZE(2) + JSON_OBJECT_SIZE(3) + JSON_OBJECT_SIZE(5) + JSON_OBJECT_SIZE(8) + 370;
      DynamicJsonBuffer jsonBuffer(bufferSize);
      JsonObject& root = jsonBuffer.parseObject(http.getString());



      const char* shortName = root["shortName"]; 
      const char* vehicleName = root["vehicleName"]; 
      const char* lineDirection = root["lineDirection"]; 
      const char* time = root["time"];



      Serial.print("Nom ligne:");
      Serial.println(shortName);
      Serial.print("Nom RER:");
      Serial.println(vehicleName);
      Serial.print("Direction:"); 
      Serial.println(lineDirection);
      Serial.print("Temps:");
      Serial.println(time);
    }
    http.end();  
  }

  delay(120000);
}
4

You probably want something like:

const char* shortName = root[0]["shortName"];

But you may want to use:

JsonDocument::is<T>()

to determine the type of the JSON object in advance, so you can then index one or more elements properly.
Read this page and the sub-links for more information.

5

My snippet is probably the arduino programming language which should be "C".

Here is the full code if you want :

The full code makes it clearer what you are doing which is why posters are asked to provide the whole program and not just a snippet

6

Thank you for your answers guys, i will try your solutions and tell you if it works!
UKHelibob, sorry for that now I know!