Hello I am having some trouble with a sketch for my gps. I have a sketch that I have seen work on the Uno but i tried it on my Due and it gives me the error "'dtostrf' was not declared in this scope." i dont know if i have to download a library or just use a different function, either was if someone could help me to solve my dilema it would be greatly appriciated 
here is the code that i am using...
if any alternative working code could be provided that would also be greatly appriciated
THANK YOU
#include <TinyGPS.h>
#include <SD.h>
#include <stdlib.h>
TinyGPS gps;
static char dtostrfbuffer[20];
int CS = 53;
int LED = 13;
//Define String
String SD_date_time = "invalid";
String SD_lat = "invalid";
String SD_lon = "invalid";
String dataString ="";
static void gpsdump(TinyGPS &gps);
static bool feedgps();
static void print_float(float val, float invalid, int len, int prec, int SD_val);
static void print_int(unsigned long val, unsigned long invalid, int len);
static void print_date(TinyGPS &gps);
static void print_str(const char *str, int len);
void setup()
{
pinMode(CS, OUTPUT); //Chip Select Pin for the SD Card
pinMode(LED, OUTPUT); //LED Indicator
//Serial interfaces
Serial.begin(115200);
Serial3.begin(4800);
//Connect to the SD Card
if(!SD.begin(CS))
{
Serial.println("Card Failure");
return;
}
Serial.print("Testing TinyGPS library v. "); Serial.println(TinyGPS::library_version());
Serial.println("by Mikal Hart");
Serial.println();
Serial.print("Sizeof(gpsobject) = "); Serial.println(sizeof(TinyGPS));
Serial.println();
Serial.println("Sats HDOP Latitude Longitude Fix Date Time Date Alt Course Speed Card Distance Course Card Chars Sentences Checksum");
Serial.println(" (deg) (deg) Age Age (m) --- from GPS ---- ---- to London ---- RX RX Fail");
Serial.println("--------------------------------------------------------------------------------------------------------------------------------------");
}
void loop()
{
bool newdata = false;
unsigned long start = millis();
// Every second we print an update
while (millis() - start < 1000)
{
if (feedgps())
newdata = true;
}
gpsdump(gps);
//Write the newest information to the SD Card
dataString = SD_date_time + "," + SD_lat + "," + SD_lon;
if(SD_date_time != "invalid")
digitalWrite(LED, HIGH);
else
digitalWrite(LED, LOW);
//Open the Data CSV File
File dataFile = SD.open("LOG.csv", FILE_WRITE);
if (dataFile)
{
dataFile.println(dataString);
Serial.println(dataString);
dataFile.close();
}
else
{
Serial.println("\nCouldn't open the log file!");
}
}
static void gpsdump(TinyGPS &gps)
{
float flat, flon;
unsigned long age, date, time, chars = 0;
unsigned short sentences = 0, failed = 0;
static const float LONDON_LAT = 51.508131, LONDON_LON = -0.128002;
print_int(gps.satellites(), TinyGPS::GPS_INVALID_SATELLITES, 5);
print_int(gps.hdop(), TinyGPS::GPS_INVALID_HDOP, 5);
gps.f_get_position(&flat, &flon, &age);
print_float(flat, TinyGPS::GPS_INVALID_F_ANGLE, 9, 5, 1); //LATITUDE
print_float(flon, TinyGPS::GPS_INVALID_F_ANGLE, 10, 5, 2); //LONGITUDE
print_int(age, TinyGPS::GPS_INVALID_AGE, 5);
print_date(gps); //DATE AND TIME
print_float(gps.f_altitude(), TinyGPS::GPS_INVALID_F_ALTITUDE, 8, 2, 0);
print_float(gps.f_course(), TinyGPS::GPS_INVALID_F_ANGLE, 7, 2, 0);
print_float(gps.f_speed_kmph(), TinyGPS::GPS_INVALID_F_SPEED, 6, 2, 0);
print_str(gps.f_course() == TinyGPS::GPS_INVALID_F_ANGLE ? "*** " : TinyGPS::cardinal(gps.f_course()), 6);
print_int(flat == TinyGPS::GPS_INVALID_F_ANGLE ? 0UL : (unsigned long)TinyGPS::distance_between(flat, flon, LONDON_LAT, LONDON_LON) / 1000, 0xFFFFFFFF, 9);
print_float(flat == TinyGPS::GPS_INVALID_F_ANGLE ? 0.0 : TinyGPS::course_to(flat, flon, 51.508131, -0.128002), TinyGPS::GPS_INVALID_F_ANGLE, 7, 2, 0);
print_str(flat == TinyGPS::GPS_INVALID_F_ANGLE ? "*** " : TinyGPS::cardinal(TinyGPS::course_to(flat, flon, LONDON_LAT, LONDON_LON)), 6);
gps.stats(&chars, &sentences, &failed);
print_int(chars, 0xFFFFFFFF, 6);
print_int(sentences, 0xFFFFFFFF, 10);
print_int(failed, 0xFFFFFFFF, 9);
Serial.println();
}
static void print_int(unsigned long val, unsigned long invalid, int len)
{
char sz[32];
if (val == invalid)
strcpy(sz, "*******");
else
sprintf(sz, "%ld", val);
sz[len] = 0;
for (int i=strlen(sz); i<len; ++i)
sz[i] = ' ';
if (len > 0)
sz[len-1] = ' ';
Serial.print(sz);
feedgps();
}
static void print_float(float val, float invalid, int len, int prec, int SD_val)
{
char sz[32];
if (val == invalid)
{
strcpy(sz, "*******");
sz[len] = 0;
if (len > 0)
sz[len-1] = ' ';
for (int i=7; i<len; ++i)
sz[i] = ' ';
Serial.print(sz);
if(SD_val == 1) SD_lat = sz;
else if(SD_val == 2) SD_lon = sz;
}
else
{
Serial.print(val, prec);
if (SD_val == 1) SD_lat = dtostrf(val,10,5,dtostrfbuffer);
else if (SD_val == 2) SD_lon = dtostrf(val,10,5,dtostrfbuffer);
int vi = abs((int)val);
int flen = prec + (val < 0.0 ? 2 : 1);
flen += vi >= 1000 ? 4 : vi >= 100 ? 3 : vi >= 10 ? 2 : 1;
for (int i=flen; i<len; ++i)
Serial.print(" ");
}
feedgps();
}
static void print_date(TinyGPS &gps)
{
int year;
byte month, day, hour, minute, second, hundredths;
unsigned long age;
gps.crack_datetime(&year, &month, &day, &hour, &minute, &second, &hundredths, &age);
if (age == TinyGPS::GPS_INVALID_AGE)
{
Serial.print("******* ******* ");
SD_date_time = "invalid";
}
else
{
char sz[32];
sprintf(sz, "%02d/%02d/%02d %02d:%02d:%02d ",
month, day, year, hour, minute, second);
Serial.print(sz);
SD_date_time = sz;
}
print_int(age, TinyGPS::GPS_INVALID_AGE, 5);
feedgps();
}
static void print_str(const char *str, int len)
{
int slen = strlen(str);
for (int i=0; i<len; ++i)
Serial.print(i<slen ? str[i] : ' ');
feedgps();
}
static bool feedgps()
{
while (Serial3.available())
{
if (gps.encode(Serial3.read()))
return true;
}
return false;
}