Nothing received from function returning array of strings

Question

My read function returns an array of strings. i.e ssid and password

String* configuration::read() {
    String rw_ssid = "";
    String rw_pswd = "";
    const int keys = 2;
    String read_ssid_pswd [keys];
    if (EEPROM.read(0) != 0) {

      for (int i = 0; i < 32; ++i) {
        rw_ssid += char(EEPROM.read(i));
      }
      for (int i = 32; i < 96; ++i) {
        rw_pswd += char(EEPROM.read(i));
      }
      Serial.print("rPASSWORD: ");
      Serial.println(rw_pswd);
      read_ssid_pswd[0] = rw_ssid;
      read_ssid_pswd[1] = rw_pswd;
      Serial.print("Sending ssid:");
      Serial.print(read_ssid_pswd[0]);
      Serial.print(" Pswd: ");
      Serial.println(read_ssid_pswd[1]);
      return read_ssid_pswd;
    } else {
      Serial.println("Data wifi not found!");
      return read_ssid_pswd;
    }
}

I can see the print in the serial monitor.

Sending ssid:SSID Pswd: password

but where this function is called from I have set it up like this:

void setup() {
  Serial.begin(115200);
  Eeprom::configuration::initialize();
  String* ssid_password = Eeprom::configuration::read();
  Serial.print(">SSID: ");
  Serial.println(ssid_password[0]);
  Serial.print(">Password: ");
  Serial.println(ssid_password[1]);
  Funcs::connection::connectWifi(ssid_password[0], ssid_password[1]);  
}

and I get thing in the prints I thought its not giving any error at compile time so it should be correct.

score 2 · Answer 1 · answered May 30 '20 at 20:09

You can't return locally defined arrays like that. The array only exists in the function, and all you do is return a pointer to where that array was. As the array has gone when you leave the function your pointer just points to garbage.

Instead you should pass an array to the function that the function then populates.

score 1 · Accepted Answer · edited Jun 02 '20 at 04:54

Majenko has it right, your String array should be allocated in Setup(). Notice that I passed back the success/failure of your initial EEPROM test as the return value.

void setup() {
  Serial.begin(115200);
  Eeprom::configuration::initialize();
  const int keys = 2;
  String ssid_password[keys];  
  if (Eeprom::configuration::read(ssid_password)) {  
    Serial.print(">SSID: ");
    Serial.println(ssid_password[0]);
    Serial.print(">Password: ");
    Serial.println(ssid_password[1]);
    Funcs::connection::connectWifi(ssid_password[0], ssid_password[1]);  
  } else {
    Serial.println("Data wifi was not found!");
  }
}

The String array is the parameter, not the return value. It is passed by reference. The copying of EEPROM chars to String doesn't need to be into temporary variables, in fact it's inefficient and pointless; it can go straight into read_ssid_pswd[0] and [1], but I didn't want to change your code excessively, and delete the debugging serial writes.

bool configuration::read(String read_ssid_pswd[]) {
    String rw_ssid = "";
    String rw_pswd = "";
    if (EEPROM.read(0) != 0) {

      for (int i = 0; i < 32; ++i) {
        rw_ssid += char(EEPROM.read(i));
      }
      for (int i = 32; i < 96; ++i) {
        rw_pswd += char(EEPROM.read(i));
      }
      Serial.print("rSSID: ");
      Serial.println(rw_ssid);
      Serial.print("rPASSWORD: ");
      Serial.println(rw_pswd);

      read_ssid_pswd[0] = rw_ssid;
      read_ssid_pswd[1] = rw_pswd;
      Serial.print("Sending ssid:");
      Serial.print(read_ssid_pswd[0]);
      Serial.print(" Pswd: ");
      Serial.println(read_ssid_pswd[1]);
      return true;
    } else {
      Serial.println("Data wifi not found!");
      return false;
    }
}

Nothing received from function returning array of strings

2 Answers2