Bug: Ethernet Library Sample Code WebClientRepeating

Development Suggestions for the Arduino Project
1

I originally posted this in http://arduino.cc/forum/index.php/topic,125510.0.html but since it appears to be a bug I will repost it here as well.

In the WebClientRepeating sample code for the Ethernet library there is a line for determining the posting interval. The line is

const unsigned long postingInterval = 60*1000;  // delay between updates, in milliseconds

The problem is the actual value of the postingInterval is wrong when I print it out (it is 4294961760). It seems to be a casting/overflow problem with the compiler/preprocessor. It looks like it is treating the 60 and 1000 as signed integers.

I broke this out into very short sample code to demonstrate:

const unsigned long postingInterval = 60*1000;
const unsigned long postingIntervalB = (long)60*1000;

void setup() {
  Serial.begin(9600);
  Serial.println(postingInterval);
  Serial.println(postingIntervalB);  
}

void loop() {}

When I run this I get back the following values:

4294961760
60000

Other Ethernet samples use 10 seconds (10*1000) and do not appear to have this problem. I assume it is because it is withing the range of an signed integer and that is how the compiler/preprocessor is treating the values.

2

I've forwarded your message to the testers to get a diagnose :slight_smile:

thanks

3

the problem with this line:

const unsigned long postingInterval = 60*1000;  // delay between updates, in millisecond

is that the two numbers (60 and 1000) are by default defined as int constants. For AVRs ints have the size of 16-bit, so the multiplication between two ints with a result that will exceed the maximum dimension for the type, generate an overflow.

The solution should be the variable cast that you propose or assigning the constant with a different type, like:

const unsigned long postingInterval = 60L*1000;  // Long typ e constant

or

const unsigned long postingInterval = 60000;  //assigning directly

This example will be fixed in the next IDE release.
Thanks for reporting!