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

Question

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

Didn't find the answer here :/

I want to send to my arduino through a serial interface (Serial.read()) a simple string of three numbers delimited with comma. Those three numbers could be of range 0-255.

Eg. 255,255,255 0,0,0 1,20,100 90,200,3

What I need to do is to parse this string sent to arduino to three integers (let's say r, g and b).

So when I send 100,50,30 arduino will translate it to

int r = 100
int g = 50
int b = 30

I tried lots of codes, but none of them worked. The main problem is to translate string (bunch of chars) to integer. I figured out that there will probably be strtok_r for delimiter purpose, but that's about it.

Thanks for any suggestions :)

Answer 1

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 + 1); // 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.