Hi Tobias, I found that if using this example, yes it will write the data every time. Which is pointless as the details are hard coded anyway.

It is only a basic example, to give an idea. using EEPROM is easier, but it only holds one byte. The preference library allows 32 bit numbers, stings etc. so once one gets used to it, it is far more versatile.

The preferences library is clever, it checks the contents of the preference, to see if it matches that of the new data and only performs a write if it is different, so behind the preferences put, is something like….

if new input is different to new input then preferences.put

so in actual fact, repeatedly using preferences.put will only actually write if the new and old data is different.

preferences also uses memory wear levelling, unlike EEPROM which reuses the same memory location, preferences moves it about

I used a library (sorry cannot think of the name right now) that solves wifi issues.
On power up, it turns on the wifi as an access point.
One connects to the esp32 with your phone and input your wifi credentials.
It then reboots and connects to your wifi.

My code is on instructables. You may want to see how I use preferences and the libray to input the wifi details.
https://www.instructables.com/Triaxial-Numechron-Clock-Updated-Accurate-Electron/

would it be better to read first compare and then write?

It seems wifi manger checks the ssid & password and connects if it can, but rather than quitting there and returning, continues to read the text box (so is the default value).

So if one saves the value to preferences first time round, it just gets overwritten.

Hi.
Thanks for noticing.
It’s fixed now.
Regards,
Sara

Because i am planning to make a product counter with ESP

daily count: 1800 pcs

trigger :1 million pcs

My concer is how to ensure the data is preserved

Thanks

Preferences uses a portion of the on-board flash as its namespace. Thus when the flash is erased, so is the space used by the Preferences library. This is how it has always been.

For more detail, see the Resources section at the end of the Preferences Tutorial on the arduino-esp32 GitHub site at: https://docs.espressif.com/projects/arduino-esp32/en/latest/tutorials/preferences.html

Thanks again for all your work.