Go Down

Topic: [SOLVED]Problem with unsigned long (Read 816 times) previous topic - next topic


Aug 18, 2011, 08:05 pm Last Edit: Aug 18, 2011, 08:33 pm by Lasse Reason: 1

I have a problem with my arduino, calculating numbers.
I am trying to count the number of seconds passed since 00:00..
Code: [Select]

unsigned long secondsElapsed = ((hour() * 3600) + (minute() * 60) + second)

if hour is between 0-8 it works, but if it's above that, secondsElapsed returns near the maximum value of an unsigned long, that is a 429496xxxx ish number..

I have almost tried anything, calculating just with numbers instead of using time, (hour * (60^2)), ((hour * 1800)*2), and I've tried with normal long, unsigned int, and so on.. But nothing seems to work, can anyone help me? :)



Make those constants 'long', so the the expression becomes 'long' and avoid overflow:

Code: [Select]
unsigned long secondsElapsed = ((hour() * 3600L) + (minute() * 60L) + second);


We're beating one another over these recent posts :)

Just FYI, you should remember from your nature/physical science course that one day has 86,400 seconds, far less than what long int or unsigned long so something else was wrong. 8 hour is about 32767, max of signed int, which is what all numerical constants are treated as without specific type case.
Serial LCD keypad panel,phi_prompt user interface library,SDI-12 USB Adapter


Thank you, Anachrocomputer.. It helped ;)

liudr: I know that the unsigned long, shouldn't have reached the limit.

Code: [Select]

unsigned long temp = 5 * 3600;

The above code worked, but.
Code: [Select]

unsigned long temp = 10 * 3600;


And neither of them is anywhere near the limit of a long, so I guess the compiler calculates it as a int.


so I guess the compiler calculates it as a int.

Correct. The compiler shoved a 10 into a 16 bit register, and 3600 into a 16 bit register, and multiplied the two registers, resulting in an overflow. The 16 bit value is then moved to a 32 bit memory location.

Had you said:
Code: [Select]
unsigned long temp = 10UL * 3600UL;
The compiler would have noticed that it needed to use 32 bit registers for the multiply operation, before moving the 32 bit result to a 32 bit memory location.
The art of getting good answers lies in asking good questions.

Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131