C# Number of days between two dates problem

Question

I have a small problem with the code below, the 'days' variable always seems to be 0 no matter how far apart the days are.

Can you see anything obviously wrong?

        System.TimeSpan span = dates[0] - dates[1]; // e.g. 12/04/2010 11:44:08 and 18/05/2010 11:52:19
        int days = (int)span.TotalDays;

        if (days > 10) //days always seems to be 0
        {
            throw new Exception("Over 10 days");
        }

Thanks

Eek exception when input values are not correct. You should return the function with a boolean if the function was successful done. — RvdK, May 18 '10 at 14:24
@RvdK, Some time has passed since you wrote that comment, but you are totally wrong here. You really should NOT litter C# code with return value error checking. That's what exceptions are for. Without exceptions, you can't chain method calls etc. If you really would like to stress input validation here, Jamie should throw ArgumentExceptions for values that are not acceptable. — JonasW, May 18 '15 at 15:28
@JonasW: indeed long time ago. I would indeed use the argument exception. Back then I did not know better... — RvdK, May 19 '15 at 05:24

score 6 · Answer 1 · answered May 18 '10 at 11:12

As you are subtracting the later date from the earlier date, according to your comments, TotalDays will be negative. In your example, -36.

Therefore a comparison of (days > 10) will fail. You should use

int days = Math.Abs((int)span.TotalDays);

Assuming you haven't set date[0] equal to date[1], there is no reason why TotalDays will be returning zero for the sample dates you have in your comments.

Petar Minchev · Answer 2 · 2010-05-18T11:19:40.920

4

The total days should be negative but in any case not zero, cause you substract the earlier date from the later date. It seems dates[0] and dates[1] are not containing what you think.

edited May 18 '10 at 11:19

answered May 18 '10 at 11:02

Petar Minchev

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TimeSpans can be negative, so it wouldn't be exactly 0. – Tesserex May 18 '10 at 11:06

score 1 · Answer 3 · answered May 18 '10 at 11:14

I just tested this:

DateTime date1 = new DateTime(2010, 12, 31);
DateTime date2 = new DateTime(2010, 1, 1);

TimeSpan timeSpan = date2 - date1;
Console.WriteLine(timeSpan.TotalDays);

This program produces the output: -364. So it should perfectly work! One question: Did you use DateTime[] for the dates-array?

BTW: days > 10 does not check if days is zero.

score 0 · Answer 4 · answered May 18 '10 at 11:07

If we assume your code looks exactly like that, and the dates array is correctly populated, then there is nothing wrong here that would cause days to be exactly zero. Maybe check that your dates array has the correct values in it? Barring that, post more code?

score 0 · Answer 5 · answered May 18 '10 at 14:15

Either do this:

System.TimeSpan span = dates[0] - dates[1]; 
int days = Math.Abs((int)span.TotalDays);

if (days > 10)
{
    throw new Exception("Over 10 days");
}

Or this:

System.TimeSpan span = dates[1] - dates[0]; 
int days = (int)span.TotalDays;

if (days > 10)
{
    throw new Exception("Over 10 days");
}

C# Number of days between two dates problem

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