Parsing RGB HexCode String for a ESP 8266

Question

I'm working on a project where my ESP8266 receives color hexCodes from the internet and then I use that color for an LED strip.

An example text that I receive is "$3#FF00FF"

However my code currently crashes whenever the B value is non-zero, so "$3#FF00FF" and "$3#FF0012" would crash it but "$3#FF0000" would not. Here is a bare bones version of my code. Also when it crashes and the ESP8266 automatic WDT does not activate either, so I am guessing it's a memory leak.

int r1 = 0;
int g1 = 0;
int b1 = 0;

void setup() {
  // boilerplate
}

void loop() {

  String data = // getting string of data from server, format is like "$3#FF0000"
  
  if (data.charAt(0) == '$' && dataLen == 9) {
    char ledStrip = data.charAt(1);
    char buffer[10];
    data.toCharArray(buffer, sizeof(buffer));

    r1 = strtol(data.substring(3, 5).c_str(), NULL, 16); // Parse hex to int
    g1 = strtol(data.substring(5, 7).c_str(), NULL, 16);

    // Note it does crash after this line but indiscriminately after
    // If I remove this line the error does not ever happening
    // So I'm assuming is a memory issue
    b1 = strtol(data.substring(7, 9).c_str(), NULL, 16);

    Serial.print("Received RGB values for Strip 1 & 2: R=");
    Serial.print(r1);
    Serial.print(", G=");
    Serial.print(g1);
    Serial.print(", B=");
    Serial.println(b1);

  }

}

Does this bare bones version crash?

n. m. could be an AI
– n. m. could be an AI

2024-05-11 01:28:17 +00:00
Commented May 11, 2024 at 1:28 — n. m. could be an AI
– n. m. could be an AI, Commented May 11, 2024 at 1:28

hello_user · Accepted Answer · 2024-05-11 03:02:39Z

1

In your code, please comfirm:

"dataLen": undefined
"buffer[10]": unused

You can using sscanf+buffer instead of string type as bellow:

    char buffer[10] = // getting data from server, format is like "$3#FF0000"
    sscanf(buffer + 3, "%2hhx%2hhx%2hhx", &r1, &g1, &b1);
    Serial.print("Received RGB values for Strip 1 & 2: R=");
    Serial.print(r1);
    Serial.print(", G=");
    Serial.print(g1);
    Serial.print(", B=");
    Serial.println(b1);

answered May 11, 2024 at 3:02

hello_user

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2 Comments

kazar4 Over a year ago

what does the hh part of hhx do?

hello_user Over a year ago

hh: 1byte scanf, so 'hhx' means: read from buffer in 1-byte hexadecimal format.

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