Simple? Code crashing

Projects Programming
1

Hi,

I have the following code:

int INT = 110;
unsigned long LAST_ACTION = 2000;
 
 
void setup()
{
    Serial.begin(9600);
    Serial.println("Hello");
}
 
void loop()
{
 
  Serial.print(millis());
  Serial.print(" - ");
  Serial.println(LAST_ACTION);
 
  if ( (millis() - LAST_ACTION) >= 2400)
  {
    INT--;
    LAST_ACTION = millis();
  }
 
  Serial.println(String(INT) + " " + String( (2400 - (millis() - LAST_ACTION))) + " ms");
  delay(100);
}

It keeps crashing AFTER the INT has reached below 100, which is really odd. Here's an example output I get from an Arduino Mega, and Arduino UNO

0 - 2000
109 2400 ms
100 - 0
109 2299 ms
201 - 0
109 2199 ms
302 - 0
109 2097 ms
403 - 0
109 1997 ms
503 - 0
109 1896 ms
605 - 0
109 1795 ms
705 - 0
109 1694 ms
806 - 0
109 1594 ms
907 - 0
109 1492 ms
1008 - 0
109 1392 ms
1108 - 0
.... miss a few ....
 
99 74 ms
26690 - 24264
98 2400 ms
26791 - 26691
98 2299 ms
26893 - 26691
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Now, If I use the following code:

  Serial.print(String(INT) + " ");
  Serial.print( (2400 - (millis() - LAST_ACTION)) );
  Serial.println(" ms");

It doesn't seem to crash. Could somebody please explain why this might be happening?

Thanks!

2

The String class operations are malloc'ing memory every time they run, and the processor only has 2k RAM to play with - in practice this makes the String class useless for a small microcontroller and is best avoided really... Running out of memory means that the machine will crash (the stack has been over-written).

3

MarkT:
The String class operations are malloc'ing memory every time they run, and the processor only has 2k RAM to play with - in practice this makes the String class useless for a small microcontroller and is best avoided really... Running out of memory means that the machine will crash (the stack has been over-written).

This is the likely answer.

You should be using a null terminated char array for strings to avoid using Strings.