Printing SD card file contents on LCD

Question

This is a part of my program which reads data from file stored in SD card and displays that on an LCD screen.

 File dataFile = SD.open("1165.txt");
 if (dataFile) {
 Serial.println("File Opened");
 lcd.clear();
 delay( 5 ); //LCD-specific M
 lcd.setCursor( 0,0 );
 while (dataFile.available()) {
 Serial.write(dataFile.read());
 lcd.write(dataFile.read());
 lcd.print(dataFile.read());
 }
 dataFile.close();
 } else {
 // if the file didn't open, print an error:
 Serial.println("error");
 }

When I look at the serial monitor it prints the contents of that file but none of these commands print what is printed in the serial monitor,

lcd.write(dataFile.read());
lcd.print(dataFile.read());

Any ideas?

Answer 1

When you call dataFile.read(), the file pointer is advanced, so you always read different bytes in each read call. Imagine the file like a book with many lines: Each time you read, you advance the current line, so with multiple calls, you never get the same data. The solution is to currently store the last read byte:

while (dataFile.available()) {
 char readByte = dataFile.read();
 Serial.write(readByte);
 lcd.write(readByte);
 lcd.print(readByte);
}

You have two calls for displaying data in the LCD, but be careful that the second call (print) might interpret your data as a number, so just remove the lcd.print(readByte) call altogether to be sure it's printing the raw character.

Answer 2

You could also implement a readLine routine, similar to:

void _readLine(File f, char *line)
{
 boolean cr_found = false;
 int p = 0;
 while (f.available()) {
 char b = f.read();
 if(b!='\r' && b!='\n')
 line[p++] = b;
 if(b == '\r') cr_found = true;
 if((b == '\n') && cr_found) break;
 }
 line[p] = '0円';
}

And read the SD file line by line, processing each one of them by its own.

char buffer[32];
while(dataFile.available()) {
 _readLine(dataFile, buffer);
 // do something with buffer
}