How to share variables across different void()

Projects Programming
1

Hi all, I'm trying to make a device that tracks motion with a GPS module, a MicroSD card module, an Arduino and a couple of switch buttons. The device is meant to track the path of a pedestrian, who walks in straight lines. The two buttons are marked "left" and "right". When the pedestrian makes a left (or right) turn, he/she presses on the "left" (or "right") button, and the Arduino saves the current GPS coordinates + "L" for left (or "R" for right).
This is my code:

#include <SPI.h>
#include <SD.h>
const int errorLED = 13;
const int statusLED = 12;
const int chipSelect = 53;
float tmFix = 0;
float lat = 0;
float longt = 0;
int addr = 0;
void setup() {
  Serial1.begin(9600);
  Serial.begin(9600);
  digitalWrite(13, LOW);
  attachInterrupt(0, left, RISING);
  attachInterrupt(1, right, RISING);
  pinMode(13, OUTPUT);
  pinMode(2, INPUT_PULLUP);
  pinMode(3, INPUT_PULLUP);
  digitalWrite(errorLED, LOW);
}

void loop() {
  String GPSdata = "";
  if (Serial1.available() > 0) {
    if (Serial1.find("$GNRMC") == true) {
      tmFix = Serial1.parseFloat();
      lat = Serial1.parseFloat();
      longt = Serial1.parseFloat();
    }
    GPSdata += String(lat);
    GPSdata += ",";
    GPSdata += String(longt);
  }
}
void left() {
  GPSdata += ",";
  GPSdata += "L";
  File dataFile = SD.open("datalog.txt", FILE_WRITE);
  dataFile.println(GPSdata);
  dataFile.close();
  digitalWrite(statusLED, HIGH);
  delayMicroseconds(500000);
  digitalWrite(statusLED, LOW);
}
void right() {
  GPSdata += ",";
  GPSdata += "R";
  digitalWrite(statusLED, HIGH);
  delayMicroseconds(500000);
  digitalWrite(statusLED, LOW);

}

and this is the error message:
"
Arduino: 1.6.6 Hourly Build 2015/08/19 10:30 (Windows 8.1), Board: "Arduino Mega or Mega 2560, ATmega2560 (Mega 2560)"

GPSparseFloat.ino: In function 'void left()':
GPSparseFloat:36: error: 'GPSdata' was not declared in this scope
GPSparseFloat.ino: In function 'void right()':
GPSparseFloat:46: error: 'GPSdata' was not declared in this scope
'GPSdata' was not declared in this scope
"

Is there a way I can share the string GPSdata across the left() and right() voids? eg make GPSdata a global string?
An help is appreciated!

2

They are functions, not voids.

eg. make GPSdata a global string?

Yes. What do you think "global" means if not that?

3

Hi, how do I make a string global?

4

Declare it outside of a function, normally at the top of the program, like these other variables

const int errorLED = 13;
const int statusLED = 12;
const int chipSelect = 53;
float tmFix = 0;
float lat = 0;
float longt = 0;
int addr = 0;

instead of inside the loop() function

5

Great, thanks, the program is working now. :slight_smile: