When using the Preferences library take into account that each entry has a max length of 1984 bytes. Defined in nvs.h line 127
|
1 2 3 |
* @param[in] value The value to set. * For strings, the maximum length (including null character) is * 1984 bytes. |
Read more
According to the Preferences Example StartCounter.ino the namespace is limited to 15 chars! This is valid not only for the preferences name, but as well for the preferences keys. For example a key name bluetooth_status will fail while the key name bluetooth_stat works fine. Example and debug output: Key name with 16 characters length:
|
1 2 3 4 5 6 7 8 9 10 11 12 |
bool bluetooth_status; Preferences preferences; preferences.begin("preferences", false); bluetooth_status = preferences.getBool("bluetooth_status", false); //NVS key bluetooth status if (bluetooth_status) { Serial.println("bluetooth status: true"); preferences.putBool("bluetooth_status", false); } else { Serial.println("bluetooth status: false"); preferences.putBool("bluetooth_status", true); } preferences.end(); |
will fail to write the key value with the following error:
|
1 2 3 |
[E][preferences.cpp:306] getUChar(): nvs_get_u8 fail: bluetooth_status NOT_FOUND bluetooth status: false [E][preferences.cpp:112] putUChar(): nvs_set_u8 fail: bluetooth_status KEY_TOO_LONG |
Changing the length of the key name to 14 characters works fine:
|
1 2 3 4 5 6 7 8 9 10 11 12 |
bool bluetooth_status; Preferences preferences; preferences.begin("preferences", false); bluetooth_status = preferences.getBool("bluetooth_stat", false); //NVS key bluetooth status if (bluetooth_status) { Serial.println("bluetooth status: true"); preferences.putBool("bluetooth_stat", false); } else { Serial.println("bluetooth status: false"); preferences.putBool("bluetooth_stat", true); } preferences.end(); |
