Arduino ESP8266 read String from EEPROM

Question

I achieve to read a String from the ESP8266 EEPROM - so far so good.

However, trying to append a second string to the just read first one does not work!

I start with having the number 2 at address 0 of the EEPROM. I read from address 0 to 6.

Here is my ESP8266.ino code :

    String readM = "";
    String appendixStr = "|||";
    Serial.print("appendixStr = ");
    Serial.println(appendixStr);
    String dailyzStr = "";
    for (int a = 0; a < 7; ++a) {           // addr 0...6
        dailyzStr += char(EEPROM.read(a));
    }
    readM += dailyzStr + appendixStr;
    Serial.print("hmmm = ");
    Serial.println(readM);

And here is what the log prints:

Clearly, I would expect hmmm = 2||| but I only get hmmm = 2

Why is it not possible to append ??

score 2 · Accepted Answer · answered Nov 09 '18 at 20:47

I would recommend to use this:

#include <EEPROM.h>
// Tell it where to store your config data in EEPROM
#define cfgStart 32
// To check if it is your config data
#define version "abc"

struct storeStruct_t{
  char myVersion[3];
  char name[32];
};

void saveConfig() {
  // Save configuration from RAM into EEPROM
  EEPROM.begin(4095);
  EEPROM.put( cfgStart, settings );
  delay(200);
  EEPROM.commit();                      // Only needed for ESP8266 to get data written
  EEPROM.end();                         // Free RAM copy of structure
}

void loadConfig() {
  // Loads configuration from EEPROM into RAM
  Serial.println("Loading config");
  storeStruct_t load;
  EEPROM.begin(4095);
  EEPROM.get( cfgStart, load);
  EEPROM.end();
  // Check if it is your real struct
  if (test.myVersion[0] != version[0] ||
      test.myVersion[1] != version[1] ||
      test.myVersion[2] != version[2]) {
    saveConfig();
    return;
  }
  settings = load;
}

// Empty settings struct which will be filled from loadConfig()
storeStruct_t settings = {
  "",
  ""
};

Use saveConfig() to save the settings struct
If you want to load from the EEPROM use loadConfig() -> it will be stored in the settings struct

Thank you, KeeyPee. Looks interesting. I just wonder: What if you don't want to read the entire EEPROM at once - but only bytes 0...6 for example ? Do you still use loadConfig then ? — iKK, Nov 09 '18 at 21:41
@iKK sorry for late response, test is just a local variable to load the eeprom in, it is specified as storestruct in loadConfig() . Just save everything you want in the struct and call saveConfig. You should retrieve your settings by loading loadConfig on program start. — KeeyPee, Nov 12 '18 at 10:06

Arduino ESP8266 read String from EEPROM

1 Answers1