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My mind is blanking out, Help with subtracting time

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Started by Concentrate April 29, 2011 10:32 PM

5 comments, last by Tachikoma 12 years, 12 months ago

Concentrate

181

Author

April 29, 2011 10:32 PM

Ex) I have two time

//fomat : day/month/year/hour/minutes/sec
31 dec 2008 23 59 56
1 jan 2009 0 0 17

and I want to find the difference in seconds;

My first though was to convert it into seconds like so :



//NOTE : month are only Dec or Jan



double toSeconds(const TimeStamp& t){

	int month = t.month == "Jan" ? 1 : 12;

	return (t.year*31556926 + month*2629743.83 + t.day * 86400 + t.min*60 + t.sec);

}

But the problem is overflow. I need another way. Any advice?

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Katie

2,255

April 29, 2011 10:37 PM

Just do it with borrowing, like you'd do this by hand.





dSeconds = aSeconds - bSeconds;

if (dSeconds<0) 

{

  dSeconds += 60;

  aMinutes -= 1;

}



etc.

PREDATOR_UK

102

April 29, 2011 10:43 PM

When you hit 60 seconds just subtract one from the minute variable likewise when you hit 60 minutes subtract one from the hour variable and set the minutes to 0.

if (minutes == 60)

{

hours -= 1;

}



if (seconds == 60)

{

minutes -= 1;

}

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alvaro

21,604

April 30, 2011 12:49 AM

Just make sure you use doubles everywhere, by putting a dot (".") at the end of each numeric constant. You shouldn't have any problems with overflow then.

Zahlman

1,682

May 01, 2011 08:11 AM

Is TimeStamp your own class? If not, where does it come from? If so, could we see it please?

alvaro

21,604

May 01, 2011 02:50 PM

Oh, wait. Overflow is not your only problem. You can't just convert from years and months to seconds by multiplying by a couple of constants.

You should just use mktime, which does precisely what you want.

Tachikoma

575

May 01, 2011 03:34 PM

Yep, what Alvaro said. Calculating the time manually is complicated, you will need to consider leap years and other quirks in the calendar system, which is pain in the arse. Use standard functions and libraries to do this.

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