Return String from Function

Projects Programming
1

I have a GPS that is spitting out strings of data, might look something like this:

String myString = "99,500,,45,W,5";

I'm trying to write a function that will extract a term from the string and return it e.g. when term = 2 it will return a string 500.

The following code works:

void setup() {
  // put your setup code here, to run once:

  Serial.begin(9600);
  String myString = "99,500,,45,W,5";
  //String altitude = stringTermFunc(myString,2);   // HOW TO RETURN A STRING FROM A FUNCTION?????
  //Serial.print(altitude);

  int Cc = commaCountFunc(myString);     // Count number of commas in String

// Create an Nx1 array with the index of each comma in the string
 
  int myArray[Cc];
  int count = 0;
  for (int i = 0; i < myString.length(); i = i + 1) {

    if (myString.charAt(i) == ',') {

        myArray[count] = i;
        Serial.print("Comma Index: ");
        Serial.println(myArray[count]);
      count = count + 1;
    }
  }

// Extract the n th term from the string where n=0 will be the first term

  int n =0;     //    Choose a Term in string to extract
  int m = n-1;  //    Index in myArray (excluding m = -1)

  if (n == 0){
  
    String myTerm = myString.substring(0,myArray[0]);
    Serial.print(myTerm);
}
  else{

    String myTerm = myString.substring(myArray[m]+1,myArray[m+1]);
    Serial.print(myTerm);

}

}

void loop() {
  // put your main code here, to run repeatedly:
  
  //NOTHING

}

// Functions

int commaCountFunc(String& myString){

  // Function that counts the number of comma delimiters in a string
  // String myString = "99,500,,45,W,5";  // Example String

  int count = 0;
  
  int i = myString.length();
  
   for (int x = 0; x<i; x = x + 1){
    
    if (myString.charAt(x) == ','){

     //commaIndex[count] = myString.indexOf(',',x);
     count = count + 1;
     
    }   
  } 
  return count;
}

I'd now like to write it into a function that takes a comma spaced string, extracts the term you want as a string or char array. But I'm having problems with this.

Does anyone have any thoughts?

Thanks,

Chris

2

Does anyone have any thoughts?

Don't use the String class?

There are lots of ways to process an array of characters, and there are many helper functions in the C string library (not the String class). Look at the include file string.h, or google for the C string library (decent tutorials here or here). Or just ask about a specific technique.

For stepping through the comma-separated fields, you could use strtok, and then use atoi or atof to convert the field characters to an integer or floating-point number:

  char     nmeaString[] = "99,500,,45,W,5"; // A C string, not the String class
  uint8_t  fieldNumber  = 0;
  char    *field        = strtok( str, "," );

  while (field != NULL) {
    Serial.print( "Field #" );
    Serial.print( fieldNumber );
    Serial.print( " = " );

    int i = atoi( field )
    Serial.print( i );
    Serial.print( ", " );

    float f = atof( field );
    Serial.println( f, 3 ); // 3 digits after the decimal point

    field = strtok (NULL, ","); // get next field
    fieldNumber++;
  }

You might want to look at the Serial Input Basics examples on the Useful Links page.

You might be interested in my GPS library, NeoGPS. It's available from the Arduino IDE Library Manager, under the menu Sketch -> Include Library -> Manage Libraries.

Cheers,
/dev