arduino-esp32/libraries/Preferences/examples/Prefs2Struct/Prefs2Struct.ino

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/*
This example shows how to use Preferences (nvs) to store a
structure. Note that the maximum size of a putBytes is 496K
or 97% of the nvs partition size. nvs has signifcant overhead,
so should not be used for data that will change often.
*/
#include <Preferences.h>
Preferences prefs;
typedef struct {
uint8_t hour;
uint8_t minute;
uint8_t setting1;
uint8_t setting2;
} schedule_t;
void setup() {
Serial.begin(115200);
prefs.begin("schedule"); // use "schedule" namespace
uint8_t content[] = {9, 30, 235, 255, 20, 15, 0, 1}; // two entries
prefs.putBytes("schedule", content, sizeof(content));
size_t schLen = prefs.getBytesLength("schedule");
char buffer[schLen]; // prepare a buffer for the data
prefs.getBytes("schedule", buffer, schLen);
if (schLen % sizeof(schedule_t)) { // simple check that data fits
log_e("Data is not correct size!");
return;
}
schedule_t *schedule = (schedule_t *) buffer; // cast the bytes into a struct ptr
Serial.printf("%02d:%02d %d/%d\n",
schedule[1].hour, schedule[1].minute,
schedule[1].setting1, schedule[1].setting2);
schedule[2] = {8, 30, 20, 21}; // add a third entry (unsafely)
// force the struct array into a byte array
prefs.putBytes("schedule", schedule, 3*sizeof(schedule_t));
schLen = prefs.getBytesLength("schedule");
char buffer2[schLen];
prefs.getBytes("schedule", buffer2, schLen);
for (int x=0; x<schLen; x++) Serial.printf("%02X ", buffer[x]);
Serial.println();
}
void loop() {}