Basic Library
Digital I/O
Analog I/O
Advanced I/O
Time
Math
Trigonometry
Random Numbers
Bits and Bytes
Interrupts
Serial Comm.
Standard Library
Ethernet
Ethernet (Server)
Ethernet (Client)
Servo Motor
Stepping Motor
Character LCD
EEPROM
SPI
I2C (Wire)
SD
SD (File Operations)
Image Processing
Periodic Operation
Clock (RTC)
Utility
SD (File Operations)
The File class allows for reading from and writing to individual files on an SD card.
available
- Description
- Check if there are any bytes available for reading from the file.
- Syntax
- file.available()
- Parameters
- file: An instance of the File class (returned by SD.open())
- Returns
- The number of bytes available (int).
close
- Description
- Close the file and ensure that any data written to it is physically saved to the SD card.
- Syntax
- file.close()
- Parameters
- None
- Returns
- None
flush
- Description
- Ensures that any bytes written to the file are physically saved to the SD card. This is done automatically when the file is closed.
- Syntax
- file.flush()
- Parameters
- None
- Returns
- None
peek
- Description
- Read a byte from the file without advancing to the next one. That is, successive calls to peek() will return the same value, as will the next call to read().
- Syntax
- file.peek()
- Parameters
- None
- Returns
- The next byte (or character), or -1 if none is available.
position
- Description
- Get the current position within the file (i.e., the location to which the next byte will be read from or written to).
- Syntax
- file.position()
- Parameters
- None
- Returns
- The position within the file (unsigned long)
- Description
- Print data to the file, which must have been opened for writing. Prints numbers as a sequence of digits, each an ASCII character (i.e., The number 123 is sent as the three characters '1', '2', '3').
- Syntax
- file.print(data)
file.print(data, BASE) - Parameters
- data: The data to print (char, byte, int, long, or string)
BASE (optional): The base in which to print numbers: BIN for binary (base 2), DEC for decimal (base 10), OCT for octal (base 8), HEX for hexadecimal (base 16). - Returns
- Byte
print() will return the number of bytes written, though reading that number is optional.
println
- Description
- Print data, followed by a carriage return and newline, to the File, which must have been opened for writing. Prints numbers as a sequence of digits, each an ASCII character (i.e., The number 123 is sent as the three characters '1', '2', '3').
- Syntax
- file.println(data)
file.println(data, BASE) - Parameters
- data: The numbers or character string to print
BASE: The base in which to print numbers (BYTE, BIN, DEC, HEX, OCT) - Returns
- Byte
println() will return the number of bytes written, though reading that number is optional.
seek
- Description
- Seek to a new position in the file, which must be between 0 and the size of the file (inclusive).
- Syntax
- file.seek(unsigned long pos)
- Parameters
- pos: The position to which to seek (unsigned long)
- Returns
- True for success, false for failure (boolean).
size
- Description
- Get the size of the file.
- Syntax
- file.size()
- Parameters
- None
- Returns
- The size of the file in bytes (unsigned long).
read
- Description
- Reads a byte from the file.
- Syntax
- file.read()
- Parameters
- None
- Returns
- The next byte (or character), or -1 if none is available (or at the end of a file).
write
- Description
- Write data or character string to the file.
- Syntax
- file.write(data)
file.write(buf, len) - Parameters
- data: The byte, char, or string (char *) to write
buf: An array of characters or bytes
len: The number of elements in buf. - Returns
- Byte
write() will return the number of bytes written, though reading that number is optional.
isDirectory
- Description
- Directories (or folders) are special kinds of files, this function reports if the current file is a directory or not.
- Syntax
- file.isDirectory()
- Parameters
- None
- Returns
- True if directory, false if file.
openNextFile
- Description
- Reports the next file or folder in a directory.
- Syntax
- file.openNextFile()
- Parameters
- None
- Returns
- char: The next file or folder in the path.
rewindDirectory
- Description
- rewindDirectory() will bring you back to the first file in the directory, used in conjunction with openNextFile().
- Syntax
- file.rewindDirectory()
- Parameters
- None
- Returns
- None
Sample Program
This sample program runs a test of all operations (write, read, get size, remove) by accessing the Micro SD on the back of the GR-KAEDE board.
#include <Arduino.h>
#include <SD.h>
void setup(){
Serial.begin(9600);
while(!Serial.available()); // wait to press key
Serial.read(); //dummy
if(!SD.begin()){
Serial.println("Card failed, or not present.");
while(1);
}
}
void loop(){
File file = SD.open("sample.txt", FILE_WRITE);
if(file){
//Write
Serial.println("Success to open sample.txt and write hello.");
file.println("Hello, my SD");
file.close();
//Read
file = SD.open("sample.txt", FILE_READ);
Serial.println("Reading file...");
while(file.available()){
Serial.print((char)file.read());
delay(50);
}
Serial.println();
//Size
Serial.print("File Size:");
Serial.println(file.size());
file.close();
digitalWrite(PIN_LED0, 0);
//Remove
Serial.println("Remove the file? y/n");
while(!Serial.available());
if(Serial.read() == 'y'){
SD.remove("sample.txt");
Serial.println("sample.txt has been removed");
}
delay(400);
} else {
Serial.println("Failed to open file.");
digitalWrite(PIN_LED0, 0);
while(1);
}
}