jsonconfig1.h

void loadConfiguration() {
 if (LittleFS.exists("/config.json")) {
  //file exists, reading and loading
  Serial.println("reading config file");
  File configFile = LittleFS.open("/config.json", "r");
  if (configFile) {
   Serial.println("opened config file");
   size_t size = configFile.size();
   // Allocate a buffer to store contents of the file.
   std::unique_ptr<char[]> buf(new char[size]);

   configFile.readBytes(buf.get(), size);
   DynamicJsonDocument doc(512);
   DeserializationError error = deserializeJson(doc, (buf.get()));
   if (error)
  Usermax0 = doc["Usermax0"];
  Usermin0 = doc["Usermax0"];
  }
  else{
    Serial.println("Failed to open config file");
  }
  configFile.close();
  Serial.print("Usermax0 :");Serial.println(Usermax0);
  Serial.print("Usermax0 :");Serial.println(Usermax0);
 }
 else{ Serial.println("The JSON file doesn't exist "); }
}

void saveConfiguration() {
 if (LittleFS.exists("/config.json")) {
  //file exists, Saving configuration
  Serial.println("saving config");
  StaticJsonDocument<512> doc;
  doc["Usermax0"] = Usermax0;
  doc["Usermin0"] = Usermin0;
  doc["Usermax1"] = Usermax1;
  doc["Usermin1"] = Usermin1;
  doc["Usermax2"] = Usermax2;
  serializeJson(doc, Serial);
  File configFile = LittleFS.open("/config.json", "w");
  if (!configFile) { Serial.println("failed to open config file for writing"); }
 }
 else{
  Serial.println("The JSON file doesn't exist ");
 }
}