Arduino (C language) parsing string with delimiter (input through serial interface)

To answer the question you actually asked, String objects are very powerful and they can do exactly what you ask. If you limit your parsing rules directly from the input, your code becomes less flexible, less reusable, and slightly convoluted.

Strings have a method called indexOf() which allows you to search for the index in the String's character array of a particular character. If the character is not found, the method should return -1. A second parameter can be added to the function call to indicate a starting point for the search. In your case, since your delimiters are commas, you would call:

int commaIndex = myString.indexOf(',');
//  Search for the next comma just after the first
int secondCommaIndex = myString.indexOf(',', commaIndex+1);

Then you could use that index to create a substring using the String class's substring() method. This returns a new String beginning at a particular starting index, and ending just before a second index (Or the end of a file if none is given). So you would type something akin to:

String firstValue = myString.substring(0, commaIndex);
String secondValue = myString.substring(commaIndex+1, secondCommaIndex);
String thirdValue = myString.substring(secondCommaIndex); // To the end of the string

Finally, the integer values can be retrieved using the String class's undocumented method, toInt():

int r = firstValue.toInt();
int g = secondValue.toInt();
int b = thirdValue.toInt();

More information on the String object and its various methods can be found int the Arduino documentation.

I think you want to do something like this to read in the data:

String serialDataIn;
String data[3];
int counter;


int inbyte;

void setup(){
  Serial.begin(9600);
  counter = 0;
  serialDataIn = String("");
}

void loop()
{
    if(serial.available){
        inbyte = Serial.read();
        if(inbyte >= '0' & inbyte <= '9')
            serialDataIn += inbyte;
        if (inbyte == ','){  // Handle delimiter
            data[counter] = String(serialDataIn);
            serialDataIn = String("");
            counter = counter + 1;
        }
        if(inbyte ==  '\r'){  // end of line
                handle end of line a do something with data
        }        
    }
}

Then use atoi() to convert the data to integers and use them.

@cstrutton -Excellent suggestion on using 'indexOf' . it saved me a ton of time for my project. One minor pointer though,

I noticed the thirdvalue did not get displayed (was coming back as ZERO). Upon playing with it little-bit and going through the doc at http://arduino.cc/en/Tutorial/StringIndexOf I realized, I can use lastIndexOf for the last value.

Here are two lines of modifications that provided correct third value.

int lastCommaIndex = myString.lastIndexOf(',');

String thirdValue = myString.substring(lastCommaIndex+1); // To the end of the string