Cookbooks
Arduino
Chapter 6. Files and I/O
Writing a text file

Arduino:
Writing a text file

How to:

To write to a text file on an SD card using Arduino, you first need to include the SD.h library, which provides the necessary functions to interact with SD cards. Make sure your Arduino board is connected to an SD card module.

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

File myFile;

void setup() {
  // Initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  
  // Check for SD card initialization
  if (!SD.begin(4)) {
    Serial.println("Initialization failed!");
    return;
  }
  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 text file write.");
    // 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
}

Sample Output:

When you run this code, the Arduino IDE Serial Monitor will display:

Initialization done.
Writing to test.txt...done.

To check if the data was correctly written, you can remove the SD card from the Arduino, insert it into a computer, and open the test.txt file to see the message “Testing text file write.”

For projects requiring more advanced file operations or processing, consider exploring additional libraries or writing custom functions tailored to your specific needs.

Reading command line argumentsWriting to standard error