Splitting a CHAR string into several peices.

Projects Programming
1

I have a project where a radio sends an RGB value to a slave device controlling some LEDs.

The signal is received as a string of 9 bytes, 3 bytes for Red, Green and Blue respectively.

I want to substring these and then use the atoi function, however my substring interpretation isnt working:

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

    Serial.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
char receivedChars[10] = " 32 64  0";
int R, G, B;

 
 char red[3];

      red[0] = receivedChars[0];
      red[1] = receivedChars[1];
      red[2] = receivedChars[2];
      R = atoi(red);
  
char green[3];
      green[0] = receivedChars[3];
      green[1] = receivedChars[4];
      green[2] = receivedChars[5];
      G = atoi(green);
  
char blue[3];
      blue[0] = receivedChars[6];
      blue[1] = receivedChars[7];
      blue[2] = receivedChars[8];     
      B = atoi(blue); 

  
       Serial.print("red is: ");
       Serial.println(red);
       Serial.print("red length: ");
       Serial.println(strlen(red));
       Serial.print("green is: ");
       Serial.println(green);
       Serial.print("green length: ");
       Serial.println(strlen(green));
       Serial.print("blue is: ");
       Serial.println(blue);
       Serial.print("blue length: ");
       Serial.println(strlen(blue));

       delay(10000);
    }

This gives the output:

red is:  32

red length: 5
green is:  64 32

green length: 8
blue is:   0 64 32

blue length: 11

Not sure how this is going so wrong. Have looked for sub-char examples however nothing I could decipher.

Thanks in advance. - Murray.

2 
      R = atoi(red);

red is NOT a string.

A string is a NULL terminated array of chars. red is NOT NULL terminated, so you should not be passing it to a function that expects a string.

3

PaulS:

      R = atoi(red);

red is NOT a string.

A string is a NULL terminated array of chars. red is NOT NULL terminated, so you should not be passing it to a function that expects a string.

Thanks for this. I'll elaborate on the problem that I am having.

In the example below I am expecting R to be 32, G to be 128 and B to be 0. What I get instead is that B is 128 due to the 'blue' char array ending up being loaded with other data. What I cannot understand is how the 'blue' char array ends up with the chars '128' in there as I am only loading it with 3 bytes and it has a size of 3.

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

    Serial.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
char receivedChars[10] = " 32128  0";
int R, G, B;

 
 char red[3];

      red[0] = receivedChars[0];
      red[1] = receivedChars[1];
      red[2] = receivedChars[2];
      R = atoi(red);
  
char green[3];
      green[0] = receivedChars[3];
      green[1] = receivedChars[4];
      green[2] = receivedChars[5];
      G = atoi(green);
  
char blue[3];
      blue[0] = receivedChars[6];
      blue[1] = receivedChars[7];
      blue[2] = receivedChars[8];     
      B = atoi(blue); 

  
       Serial.print("red is: ");
       Serial.println(red);
       Serial.print("red length: ");
       Serial.println(strlen(red));
       Serial.print("R is: ");
       Serial.println(R);
       Serial.print("green is: ");
       Serial.println(green);
       Serial.print("green length: ");
       Serial.println(strlen(green));
       Serial.print("G is: ");
       Serial.println(G);
       Serial.print("blue is: ");
       Serial.println(blue);
       Serial.print("blue length: ");
       Serial.println(strlen(blue));
       Serial.print("B is: ");
       Serial.println(B);

       delay(10000);
    }void setup() {
  // put your setup code here, to run once:

    Serial.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
char receivedChars[10] = " 32128  0";
int R, G, B;

 
 char red[3];

      red[0] = receivedChars[0];
      red[1] = receivedChars[1];
      red[2] = receivedChars[2];
      R = atoi(red);
  
char green[3];
      green[0] = receivedChars[3];
      green[1] = receivedChars[4];
      green[2] = receivedChars[5];
      G = atoi(green);
  
char blue[3];
      blue[0] = receivedChars[6];
      blue[1] = receivedChars[7];
      blue[2] = receivedChars[8];     
      B = atoi(blue); 

  
       Serial.print("red is: ");
       Serial.println(red);
       Serial.print("red length: ");
       Serial.println(strlen(red));
       Serial.print("R is: ");
       Serial.println(R);
       Serial.print("green is: ");
       Serial.println(green);
       Serial.print("green length: ");
       Serial.println(strlen(green));
       Serial.print("G is: ");
       Serial.println(G);
       Serial.print("blue is: ");
       Serial.println(blue);
       Serial.print("blue length: ");
       Serial.println(strlen(blue));
       Serial.print("B is: ");
       Serial.println(B);

       delay(10000);
    }

Output:

red is:  32U
red length: 5
R is: 32
green is: 128 32U
green length: 8
G is: 128
blue is:   0128 32U
blue length: 11
B is: 128
4 
char red[4];
red[0] = receivedChars[0];
red[1] = receivedChars[1];
red[2] = receivedChars[2];
red[3] = '\0'; //terminate!
R = atoi(red);
5

PaulS already identified the problem. Make your arrays four characters long and set the last character to null (zero) before you call atoi.

Oops. too slow :wink:

6

Many thanks to all.