char table in a function retains values between calls without static [SOLVED]

Projects Programming
1

Hi,

If you take a look at the code below, it works perfectly, even if buff[] is not declared static.

Why?

bool table[3][3] = {false, false, false,
                    false, false, false,
                    false, false, false};

bool readMonitor() {
  char buf[3];
  static byte i = 0;
  if (Serial.available()>0){ buf[i] = Serial.read(); i++; }
  if (int(buf[i-1]) == 13) {
    i = 0;
    table[buf[0]-48][buf[1]-48] = true;
    return true;
  }
  return false;
}


void setup() {
  Serial.begin(9600);
}

void loop() {
  if (readMonitor()) {
    for (int i = 0 ; i < 3 ; i++) {
      for (int j = 0 ; j < 3 ; j++) Serial.print(table[i][j]);
      Serial.println();
    }
    Serial.println();
  }
}
2

You got lucky.

Ever hear the phrase "works like a charm" ?

How often do charms work?
Would you rely on that?

3

The stack locations where buff[] is stored just don't happen to be overwritten by other code.

4

So it is placed on the stack.

Thanks it makes sense,

Jacques