// we need fundamental FILE definitions and printf declarations
#include <stdio.h>
#include <avr/pgmspace.h>

// create a FILE structure to reference our UART output function

static FILE uartout = {0} ;

// create a output function
// This works because Serial.write, although of
// type virtual, already exists.
static int uart_putchar (char c, FILE *stream)
{
    Serial.write(c) ;
    return 0 ;
}

void setup(void)
{
   // Start the UART
   Serial.begin(9600) ;

   // fill in the UART file descriptor with pointer to writer.
   fdev_setup_stream (&uartout, uart_putchar, NULL, _FDEV_SETUP_WRITE);

   // The uart is the standard output device STDOUT.
   stdout = &uartout ;
}

void loop(void)
{
    int seconds ;

    // wait 1000 milliseconds
    delay(1000) ;

    seconds = millis() / 1000 ;

    // use flash storage for the format string
    printf_P(PSTR("Alive %d sec\n"), seconds);

/*
    // without printf_P(), you would do this:
    Serial.print(F("Alive ")) ;
    Serial.print(seconds) ;
    Serial.println(F(" sec")) ;
*/

#if 0
    // you can explicitly use a FILE structure like this:
    fprintf_P( &uartout, PSTR("Alive %d sec\n"), seconds ) ;
#endif
}