Reading file from SPIFFS in nodemcu using ArduinoJson

Question

#include <ArduinoJson.h> 
#include <FS.h> 
/* Set these to desired credentials in runtime */
struct Config {
 String ssid = "";
 String pass = "";
 bool hFlag = false;
};
void setup() {
 // put your setup code here, to run once:
 Serial.begin(115200);
 Serial.println("");
 delay(1000);
 //allows serving of files from SPIFFS
 Serial.println("Mounting FS...");
 if (!SPIFFS.begin()) {
 Serial.println("Failed to mount file system");
 return;
 }
 if (readConfigFile("/LaSt.json", false)) {
 Serial.println("Config read");
 } else {
 Serial.println("Failed to read config");
 }
}
bool readConfigFile(char* fileName, bool whichFile)
{
 File configFile = SPIFFS.open(fileName, "r");
 if (!configFile) {
 Serial.println("Failed to open config file");
 return false;
 }
 size_t size = configFile.size();
 if (size > 1024) {
 Serial.println("Config file size is too large");
 return false;
 }
 // Allocate the memory pool on the stack.
 // Use arduinojson.org/assistant to compute the capacity.
 StaticJsonBuffer<256> jsonBuffer;
 // Parse the root object
 JsonObject &root = jsonBuffer.parseObject(configFile);
 if (!root.success())
 Serial.println(F("Failed to read file, using default configuration"));
 // Copy values from the JsonObject to the Config
 Config.ssid = root["ssid"];
 Config.pass = root["pass"];
 if (whichFile)
 {
 Config.hFlag = root["hFlag"];
 }
 // We don't need the file anymore
 configFile.close();
 return true;
}

Compile gives error in Copy values from the JsonObject to the Config section. Error: expected unqualified-id before '.' token.

Want to read file from SPIFFS, and store in variable to use.

• Juraj: Config is type. you do not have an instance of it

Answer 1

Your code at the top:

struct Config {
 String ssid = "";
 String pass = "";
 bool hFlag = false;
};

defines a variable "type". It's like making a new int or bool, but yours is called struct Config.

After making the type, you need to create declare an instance of it.

struct Config cfg;

Then, you refer to the one you created:

 // Copy values from the JsonObject to the Config struct named cfg
 cfg.ssid = root["ssid"];
 cfg.pass = root["pass"];
 if (whichFile)
 {
 cfg.hFlag = root["hFlag"];
 }

Note that a particular issue with ArduinoJSON and Strings is that you may get an error like:

error: ambiguous overload for 'operator=' (operand types are 'String' and 'ArduinoJson::JsonObjectSubscript<const char*>')

There is an ArduinoJSON FAQ entry that states

Most of the time you can rely on implicit casts.

But there is one notable exception: when you convert a JsonVariant to a String.

For example:

String ssid = network["ssid"];
ssid = network["ssid"];

The first line will compile but the second will fail with the following error:

error: ambiguous overload for 'operator=' (operand types are 'String' and 'ArduinoJson::JsonObjectSubscript<const char*>')

The solution is to remove the ambiguity with any of the following replacement:

ssid = (const char*)network["ssid"];
ssid = network["ssid"].as<const char*>();
ssid = network["ssid"].as<String>();

• Dr.PB: ambiguous overload for 'operator=' (operand types are 'String' and 'ArduinoJson::Internals::JsonObjectSubscript<const char*>')
• Dr.PB: link1, link2
• jose can u c: Are you meaning to ask a new question?
• Dr.PB: No, just mentioned that in the particular case, string variable type will give the error, and the workarounds are given in the links. However, those workarounds also produce warnings.

Answer 2

 
#include FS.h
#include ESP8266WiFi.h
#include ArduinoJson.h 
/* Set these to desired credentials in runtime */
 String ssid = "tttttttt";
 String pass = "ssssssss";
#define fileName "/LaSt.json"
DynamicJsonBuffer jsonBuffer;
void setup() {
 // put your setup code here, to run once:
 Serial.begin(115200);
 Serial.println("");
 delay(1000);
 //allows serving of files from SPIFFS
 Serial.println("Mounting FS...");
 if (SPIFFS.begin()) {
 if (SPIFFS.exists(fileName)) {
 File subscribedUsersFile = SPIFFS.open(fileName, "r");
 delay(10);
 String file_content = subscribedUsersFile.readString();
 JsonObject& users = jsonBuffer.parseObject(file_content);
 if(users.containsKey("ssid")) {ssid=users["ssid"].as();} 
 if(users.containsKey("pass")) {pass=users["pass"].as();}
 subscribedUsersFile.close();
 users.prettyPrintTo(Serial);
 }
else {
 // Create empty file (w+ not working as expect)
 File subscribedUsersFile = SPIFFS.open(fileName, "a+");
 JsonObject& users = jsonBuffer.createObject();
 users.set("ssid", ssid);
 users.set("pass", pass);
 users.printTo(subscribedUsersFile);
 users.printTo(Serial);
 subscribedUsersFile.close();
 Serial.println("New Config File Created...\n");
 users.prettyPrintTo(Serial); 
 } 
 }
}

• MichaelT: Answer could be improved by adding a sentence or two of explanation!! Please consider.