#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(10)) {
  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("This is a test file :)");
  myFile.println("testing 1, 2, 3.");
 
  for (int i = 0; i < 20; i++) {
    myFile.println(i);
  }
 
  // close the file:
  myFile.close();
 
  Serial.println("done.");
  } else {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
  }
}
 
void loop() {
 // nothing happens after setup
}

<code c++> #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(10)) {
  Serial.println("initialization failed!");
  while (1);
}

Serial.println("initialization done.");

// 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

}

<code>