file.parseInt();

thanks a lot !!!

file->Examples->Preferences

https://github.com/espressif/arduino-esp32/blob/master/libraries/Preferences/examples/StartCounter/StartCounter.ino

@cepics
Have you tried playing with the sd read and write examples?

yes this one

/*
  SD card read/write

 This example shows how to read and write data to and from an SD card file
 The circuit:
 * SD card attached to SPI bus as follows:
 ** MOSI - pin 11
 ** MISO - pin 12
 ** CLK - pin 13
 ** CS - pin 4 (for MKRZero SD: SDCARD_SS_PIN)

 created   Nov 2010
 by David A. Mellis
 modified 9 Apr 2012
 by Tom Igoe

 This example code is in the public domain.

 */

#include <SPI.h>
#include <SD.h>

File myFile;

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }


  Serial.print("Initializing SD card...");

  if (!SD.begin(4)) {
    Serial.println("initialization failed!");
    while (1);
  }
  Serial.println("initialization done.");

  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  myFile = SD.open("test.txt", FILE_WRITE);

  // if the file opened okay, write to it:
  if (myFile) {
    Serial.print("Writing to test.txt...");
    myFile.println("testing 1, 2, 3.");
    // close the file:
    myFile.close();
    Serial.println("done.");
  } else {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
  }

  // re-open the file for reading:
  myFile = SD.open("test.txt");
  if (myFile) {
    Serial.println("test.txt:");

    // read from the file until there's nothing else in it:
    while (myFile.available()) {
      Serial.write(myFile.read());
    }
    // close the file:
    myFile.close();
  } else {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
  }
}

void loop() {
  // nothing happens after setup
}

it compile but the serial monitor say:
error opening test.txt

right now, with an example from here, I can write an int variable in a file on sd

#include <M5Stack.h>
int cal = 2000;


void setup() {

  M5.begin();
  Wire.begin();

  Serial.begin(115200);

  File file = SD.open("/cal.txt", FILE_WRITE);
  if (!file) {
    Serial.println("Failed to open file for writing");
    return;
  }
  if (file.print(cal)) {
    Serial.println("File written");
  } else {
    Serial.println("Write failed");
  }

}

void loop() {
  // put your main code here, to run repeatedly:

}

and I can read the file with

#include <M5Stack.h>
int ch;

void setup() {

  M5.begin();
  Wire.begin();

  Serial.begin(115200);

  File file = SD.open("/cal.txt");
  if (!file) {
    Serial.println("Failed to open file for reading");
    return;
  }

  Serial.print("Read from file: ");
  M5.Lcd.print("Read from file: ");
  while (file.available()) {
    ch = file.read();
    Serial.write(ch);
    M5.Lcd.write(ch);
  }
}


void loop() {
  // put your main code here, to run repeatedly:

}

but I can't use the "ch" variable ..

if I add, on the "read" sketch

int y = ch + 2000;
Serial.print(y);

in the serial monitor I have:

M5Stack initializing...O�������
Read from file: 2000
2048

2048 instead of 4000

now I'm searching how to convert ASCII to binary

thanks for interest..

How many cycle before dead of flash partition?

I'm interested too

I'm trying this sketch:

// http://forum.m5stack.com/topic/184/problems-writing-to-sd-card
#include <M5Stack.h>

//Micro SD / TF Card Test


String cal;
String lum;
String unit;

bool brght = 0;
bool ftmt = 1;

int x = 1680;

void listDir(fs::FS &fs, const char * dirname, uint8_t levels) {

  // Print blank line on screen
  M5.Lcd.printf(" \n  ");
  M5.Lcd.printf(" \n  ");

  Serial.printf("Listing directory: %s\n", dirname);
  M5.Lcd.printf("Listing directory: %s\n", dirname);

  File root = fs.open(dirname);
  if (!root) {
    Serial.println("Failed to open directory");
    M5.Lcd.println("Failed to open directory");
    return;
  }
  if (!root.isDirectory()) {
    Serial.println("Not a directory");
    M5.Lcd.println("Not a directory");
    return;
  }

  File file = root.openNextFile();
  while (file) {
    if (file.isDirectory()) {
      Serial.print("  DIR : ");
      M5.Lcd.print("  DIR : ");
      Serial.println(file.name());
      M5.Lcd.println(file.name());
      if (levels) {
        listDir(fs, file.name(), levels - 1);
      }
    } else {
      Serial.print("  FILE: ");
      M5.Lcd.print("  FILE: ");
      Serial.print(file.name());
      M5.Lcd.print(file.name());
      Serial.print("  SIZE: ");
      M5.Lcd.print("  SIZE: ");
      Serial.println(file.size());
      M5.Lcd.println(file.size());
    }
    file = root.openNextFile();
  }
}

void readFile(fs::FS &fs, const char * path) {
  Serial.printf("Reading file: %s\n", path);
  M5.Lcd.printf("Reading file: %s\n", path);

  File file = fs.open(path);
  if (!file) {
    Serial.println("Failed to open file for reading");
    M5.Lcd.println("Failed to open file for reading");
    return;
  }

  Serial.print("Read from file: ");
  M5.Lcd.print("Read from file: ");
  while (file.available()) {
    int ch = file.read();
    Serial.write(ch);
    M5.Lcd.write(ch);
  }
}

void writeFile(fs::FS &fs, const char * path, const char * message) {
  Serial.printf("Writing file: %s\n", path);
  M5.Lcd.printf("Writing file: %s\n", path);

  File file = fs.open(path, FILE_WRITE);
  if (!file) {
    Serial.println("Failed to open file for writing");
    M5.Lcd.println("Failed to open file for writing");
    return;
  }
  if (file.print(message)) {
    Serial.println("File written");
    M5.Lcd.println("File written");
  } else {
    Serial.println("Write failed");
    M5.Lcd.println("Write failed");
  }
}

void setup() {

  M5.begin();
  Wire.begin();

  Serial.begin(115200);

  // Lcd display
  M5.Lcd.setBrightness(100);
  M5.Lcd.fillScreen(BLACK);
  M5.Lcd.setCursor(0, 10);
  M5.Lcd.setTextColor(WHITE);
  M5.Lcd.setTextSize(2);

  // Page Header
  M5.Lcd.fillScreen(BLACK);
  M5.Lcd.setCursor(0, 05);
  M5.Lcd.printf("Testing SD Card Functions:\r\n");

  /////////////////////////////////////////////////////////////////////////
  cal = String("cal = ") + String(x) + "\r\n";
  lum = String("lum = ") + String(brght) + "\r\n";
  unit = String("unit = ") + String(ftmt) + "\r\n";

  writeFile(SD, "/cal.txt", cal.c_str()); // questa funziona!!!!
  writeFile(SD, "/lum.txt", lum.c_str()); // questa funziona!!!!
  writeFile(SD, "/unit.txt", unit.c_str()); // questa funziona!!!!
  /////////////////////////////////////////////////////////////////////////

  M5.Lcd.printf("");
  // Print blank line on screen
  M5.Lcd.printf(" \n  ");
  // Print blank line on screen
  M5.Lcd.printf(" \n  ");

  readFile(SD, "/cal.txt");
  readFile(SD, "/lum.txt");
  readFile(SD, "/unit.txt");

}

void loop() {

  // put your main code here, to run repeatedly:

  M5.update();
}

but I can't understand how to read from sd and use the variables in the sketch..
I need to read and write two boolean state and one int variables ..
I'm a newbi and all the sketch I found on line that use sd.h library doesn't work on M5Stack

if I upload read/write arduino sd example, this is the serial monitor output:

error opening test.txt

please help

thanks a lot

ESP32's have something called NVM, which stores key-value pairs in another partition of the same flash. In the Arduino world, "Preferences.h" provides a wrapper to use these functions. Have a look here for an example that stores a value (the number of times the ESP was booted) in flash.

#include <EEPROM.h>
int address = 0;

 EEPROM.begin(512);
  
byte x = sonar.convert_cm(echoTime);
  delay(1000);
  EEPROM.write(address, x);
  delay(1000);
  EEPROM.commit();
  delay(1000);

  x = EEPROM.read(address);
  delay (500);

how can I do to save/read x variable on sd with m5?

tnks a lot