Nested arrays and structures

[simonemarin]

Describe the issue
I am trying to parse an array inside the json object and setting the data in 2 structures.
JSON model:

{
    "cameras": [
      {
        "viscaip": "192.168.5.163",
        "port": 1259,
        "channel": 1,
        "profile": "0"
      },
      {
        
        "viscaip": "192.168.5.163",
        "port": 1259,
        "channel": 10,
        "profile": "0"
      }
    ],
    "hostip": "192.168.5.102",
}

Troubleshooter report
Here is the report generated by the ArduinoJson Troubleshooter:

ArduinoJson Troubleshooter's report

1. The issue happens at compile time
2. The error is not in the list

Environment
Here is the environment that I'm using':

• Microconroller: ESP32
• Core/runtime: ESP32 2.0
• IDE: Arduino IDE 1.8.19

Reproduction
Here is a small snippet that demonstrate the problem.

struct Camera {
  char viscaip[16];
  int port;
  int channel;
  char HEXpan[8];
  char HEXtiltUp[8];
  char HEXtiltDown[8];  
};
struct Config {
  char hostip[16];
  Camera* cam[];
};
Config config;
  StaticJsonDocument<512> doc;
  DeserializationError error = deserializeJson(doc, file);
  JsonObject camera = doc["cameras"];
  for (JsonObject::iterator it=camera.begin(); it!=camera.end(); ++it) {
    Log.noticeln("1 camera here");
    Serial.println(camera["channel"].as<int>());
    config.cam[it]->channel = camera["channel"].as<int>(); // lost here ;)
  }

Program output
Expected output:
(apparently I get the data right but I cannot set the structure correctly

Actual output:

1
10

[simonemarin]

So I have added my own counter but isn't there a way to get the index of the current item?

  int counter = 0;
  for (JsonObject camera : doc["cameras"].as<JsonArray>()) {
    Log.noticeln("1 camera here");
    Serial.println(camera["channel"].as<int>());
    config.cam[counter].channel = camera["channel"].as<int>();
    counter++;
  }

[bblanchon]

Hi @simonemarin,

No, there is no way to get the index from the nested object.
Adding a counter, as you did, is the right solution.

Did you solve your original problem?

Best regards,
Benoit

[simonemarin]

I am still failing ad adding the values from json to the structure:

struct Camera {
    char viscaip[16];
    int port;
    int channel;
    char HEXpan[8];
    char HEXtiltUp[8];
    char HEXtiltDown[8];  
};

struct Config {
    char hostip[16];
    Camera* cam[];
};

Config config;
Camera cam[10]; //seems like I HAVE to set a maximum size

StaticJsonDocument<512> doc;
DeserializationError error = deserializeJson(doc, file);
JsonObject camera = doc["cameras"];
for (JsonObject::iterator it=camera.begin(); it!=camera.end(); ++it) {
    Log.noticeln("1 camera here");
    Serial.println(camera["channel"].as<int>());
    config.cam[it]->channel = camera["channel"].as<int>(); // lost here ;)
}

readFile(SPIFFS, filename, config);

void readFile(fs::FS &fs, const char * path, Config &config) {

  File file = fs.open(path);
  if (!file) {
    Log.errorln("Failed to open file for reading");
    return;
  }

  StaticJsonDocument<1024> doc;

  // Deserialize the JSON document
  DeserializationError error = deserializeJson(doc, file);
  if (error)
    Log.errorln(F("Failed to read file, using default configuration"));

  
  for (JsonObject camera : doc["cameras"].as<JsonArray>()) {
    Log.noticeln("Json camera with channel: %d", camera["channel"].as<int>());
    config.cam[cam_counter].channel = camera["channel"].as<int>();
    cam_counter++;
  }

  for (int i = 0; i < cam_counter; i++) {
    Log.noticeln("Iteration %d, struct camera channel: %d", i, cam[i].channel);
  }
  
  Log.noticeln("Total cameras: %d", cam_counter);

}

I get :

I: Json camera with channel: 1
I: Json camera with channel: 10
I: Iteration 0, struct camera channel: 0
I: Iteration 1, struct camera channel: 0
I: Total cameras: 2

So something is wrong in the way I set the data.

[simonemarin]

yay
config.cam[cam_counter].channel = camera["channel"].as<int>();
should be
cam[cam_counter].channel = camera["channel"].as<int>();
surely your book will come at hand ;)

[bblanchon]

Hi @simonemarin,

From your last message, I understand that your problem is fixed, so I'm going to close this issue.

For simple configurations files, you can look at the JsonConfigFile.ino example.
For complex configurations, look at the "Configuration in SPIFFS" case study in Mastering ArduinoJson: it shows how to leverage custom converters to support nested objects.

@simonemarin, thank you very much for purchasing my book; your support is greatly appreciated.
Let me know if you have any remarks about the book.

Best regards,
Benoit