Writing Char to Arduino EEPROM

Question

I'm having a problem passing data to EEPROM. It seemed to be not accepting a char variable. I'm doing exactly what is told here: https://www.arduino.cc/en/Reference/EEPROMPut

So my this is my Object Structure

struct DeviceDataObject {
  bool flag;
  char data[20];
  char data2[20];
  int rate1;
  int rate2;
  int rate3;
};

So as I test with:

int RATES[3] = {300, 1500, 3600};
DeviceDataObject new_data = {true, "Data1Sample", "Sample2", RATES[0], RATES[1], RATES[2]};
WRITE_Device(new_data);

Here's my writing function

void WRITE_Device(DeviceDataObject data) {
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }
  int eeAddress = 0;
  float f = 123.456f;  //Variable to store in EEPROM.
  EEPROM.put(eeAddress, f);
  eeAddress += sizeof(float); //Move address to the next byte after float 'f'.
  EEPROM.put(eeAddress, data);
  //Serial.println("Memory Data Updated");
}

Everything seemed to be OK. But if I replace "Data1Sample" and "Sample2" with a variable, EEPROM's data seemed to be changed in incorrectly.

void ChangeValue(String value) {
        int RATES[3] = {300, 1500, 3600};
        char charBuf[20];
        value.toCharArray(charBuf, 20); //Convert to char

        DeviceDataObject new_data = {true, "", {charBuf}, RATES[0], RATES[1], RATES[2]}
        WRITE_Device(new_data); 
}

What could be the mistake?

How do you know that it isn't being written correctly? – stark Aug 12 '18 at 13:05 — stark, Aug 12 '18 at 13:05

score 0 · Answer 1 · answered Aug 12 '18 at 11:28

0

Looks like a pointer problem, try this

void ChangeValue(String value) {
        int RATES[3] = {300, 1500, 3600};
        DeviceDataObject new_data = {true, "", "", RATES[0], RATES[1], RATES[2]}
        value.toCharArray(new_data.data2, 20); //Convert to char

        WRITE_Device(new_data); 
}

(you were creating a string where the first character was the pointer to your stack variable charBuf, rather than copying the string)

answered Aug 12 '18 at 11:28

cguest

71
5

it's not a pointer problem but a struct initialization problem – phuclv Aug 12 '18 at 11:51

score 0 · Answer 2 · answered Aug 14 '18 at 16:37

A somewhat long-winded approach would be to write each element of the structure to EEPROM individually. The code would look something like this and should allow you to isolate any issues more effectively.

ee_address = 0;

EEPROM.put(ee_address, new_data.flag);
ee_address += sizeof(new_data.flag);  // Update address to store next variable

EEPROM.put(ee_address, new_data.data);
ee_address += sizeof(new_data.data);

EEPROM.put(ee_address, new_data.data2);
ee_address += sizeof(rawdata.data2);

EEPROM.put(ee_address, new_data.rate1);
ee_address += sizeof(new_data.rate1);

EEPROM.put(ee_address, new_data.rate2);
ee_address += sizeof(new_data.rate2);

EEPROM.put(ee_address, new_data.rate3);
ee_address += sizeof(rawdata.rate3);

This will make it easier to troubleshoot whether variables are not being written to EEPROM correctly or whether the issue stems from something else.

This is the approach I typically take when storing structures which I have defined to the EEPROM, as it gives more control when retrieving this information from the EEPROM at a later point.

I'll be the first to admit this is perhaps not the most elegant solution, but it should help address your issues.

Writing Char to Arduino EEPROM

2 Answers2