Serial.write() prints a variable twice

Question

I have this code:

#include <TinyGPS++.h>
#include <SoftwareSerial.h>
#define GPS_RX_PIN 2
#define GPS_TX_PIN 3
TinyGPSPlus gps;
SoftwareSerial ss(GPS_RX_PIN, GPS_TX_PIN);
void setup()
{
 Serial.begin(9600);
 ss.begin(4800); 
}
char clat[11];
char clng[11];
void loop()
{
 bool isGpsLocationValid = false;
 do
 { 
 while (ss.available()>0)
 {
 char c = byte(ss.read());
 if (gps.encode(c)) 
 { 
 if (gps.location.isValid())
 {
 dtostrf(gps.location.lat(), 11, 6, clat);
 dtostrf(gps.location.lng(), 11, 6, clng);
 isGpsLocationValid = true;
 }
 } 
 }
 } while (isGpsLocationValid == false);
 Serial.write(clat);
 Serial.println();
 Serial.write(clng);
}

Now when all is done, the clng value is printed twice in the serial monitor. The value i get is in this format:

27.275869 15.151013
 15.151013

As you can see, clng is printed twice. Any ideas why is that?

• Peter Bloomfield: I think your question may already be answered here: arduino.stackexchange.com/questions/1197/…

Answer 1

The width parameter to dtostrf() is the width of the resulting string NOT including the null terminator. So you are overflowing the array.

Change:

char clat[11];
char clng[11];

to

char clat[12];
char clng[12];

and it should work.

• user1584421: bear in mind, my number is this : 27.275869 . and i have declared 11 digits. i think they are more than enough. i will provide more feedback on this tomorrow
• Craig: The width parameter is the minimum width not the maximum width. See the docs. If you have signed lat/long values you will need 11 characters plus the null terminator. Unsigned will only need 10 plus the null.
• user1584421: 2 digits + 1 sign + 1 dot + 6 decimal digits + 1 NULL = 11. Why do i need to declare more?
• jfpoilpret: Because dtostrf will pad the result string with spaces so that it is at least 11 characters long, so you need 12 chars in your variable. Instead of arguing, you should just do it and see that it works with 12.
• user1584421: I did with up to 14 digits and the results remain the same