teensy pointer on input string - pointers

Question

Currently a student in college, decided to jump ahead of my programming class and have a little fun with pointers. This is supposed to take a specific serial input and change the state of three LED's I have attached to the Teensy++2.0. However it seems to be just giving me back the first input.
http://arduino.cc/en/Serial/ReadBytesUntil
This is my reference for the ReadBytesUntil() The input goes #,#,### (1,1,255 being an example)
I guess basically my question is, does ReadBytesUntil() deal with commas? And if so, whats going on here?
EDIT -- I asked my teacher and even he has no clue why it doesn't work.
char *dataFinder(char *str){
while (*str != ','){
str++;
}
str++;
return str;
}
void inputDecoder(){
str = incomingText;
whichLED = *str;
dataFinder(str);
onoff = *str;
dataFinder(str);
powerLevel = *str;
}
void loop(){
int length;
if (Serial.available() > 0 ){ //this is basically: if something is typed in, do something.
length = Serial.readBytesUntil(13,incomingText, 10); //reads what is typed in, and stores it in incomingVar
incomingText[length]=0; ///swapping out cr with null
inputDecoder();
//ledControl();
Serial.print("Entered:");
//incomingText[9]=0;
Serial.println(incomingText); //Here for testing, to show what values I'm getting back.
Serial.println(whichLED);
Serial.println(onoff);
Serial.println(powerLevel);
}
delay(1000);
}

Answer 1

The str in inputDecoder() is from the global scope and is not the same str in dataFinder(), which has local scope.
Imagine this ASCII picture is the layout of memory:
str
+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+-----+-----+
| * | | | | ... | 1 | , | 1 | , | 2 | 5 | 5 | \n |
+--|--+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+-----+-----+
|
|
\-----------------------------^
When you pass str to dataFinder() it creates a copy of the pointer, which I'll call str'
str str'
+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+-----+-----+
| * | | * | | ... | 1 | , | 1 | , | 2 | 5 | 5 | \n |
+--|--+-----+--|--+-----+ +-----+-----+-----+-----+-----+-----+-----+-----+
| \-----------------^
|
\-----------------------------^
When dataFinder() increments str it is really altering str'
str str'
+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+-----+-----+
| * | | * | | ... | 1 | , | 1 | , | 2 | 5 | 5 | \n |
+--|--+-----+--|--+-----+ +-----+-----+-----+-----+-----+-----+-----+-----+
| \-----------------------------^
|
\-----------------------------^
Then, when you return to inputDecoder() you dereference str which is still pointing at the start of the string.
You can either assign the value of str' back to the global str using:
str = dataFinder(str);
or change dataFinder() so it does not take an argument, therefore not copying the variable.