C# check if Datetime.now is a specific time

Question

i want to check if the current time is a specific time so for example if the current time is 13:13:13 it would beep

var xx = new DateTime(2018,10,8,13,19,50);

while (true)
{
    if (DateTime.Now == xx)
        Console.Beep();
}

but it is not working

You actually check if `DateTime.Now == 2018-10-18 13:19:50.0000000` there's a *small probability* of `Beep` — Dmitry Bychenko, Oct 08 '18 at 12:22
You probably need to make it compare only down to the seconds value, otherwise the milliseconds will be unlikely to match. — McGaz, Oct 08 '18 at 12:25
I would use a scheduled task for this or, if you can't use them, a System.Timers.Timer. You just have to calculate the time from now until this specific time. Then handle it's [`Elapsed` event](https://learn.microsoft.com/en-us/dotnet/api/system.timers.timer.elapsed?redirectedfrom=MSDN&view=netframework-4.7.2) — Tim Schmelter, Oct 08 '18 at 12:26
you can check for an interval, e.g. Math.Abs(DateTime.Now.Subtract(xx).TotalSeconds) <= 1 — KMoussa, Oct 08 '18 at 12:26

bommelding · Accepted Answer · 2018-10-08T12:37:52.717

3

Give your CPU a break.

static void Main(string[] args)
{
    var target = DateTime.Now.AddMinutes(1);  // test data

    var aTimer = new System.Timers.Timer((target - DateTime.Now).TotalMilliseconds);
    aTimer.Elapsed += (s, e) => { Console.Beep(); };
    aTimer.Enabled = true;

    Console.WriteLine("Wait a minute...");
    // time to do something useful
    Console.ReadLine();
}

edited Oct 08 '18 at 12:37

answered Oct 08 '18 at 12:32

bommelding

2,969
9
14

Do not forget to `Dispose` the `Timer` instance: `aTimer.Elapsed += (s, ee) => {(s as System.Timers.Timer)?.Dispose(); Console.Beep(); };` – Dmitry Bychenko Oct 08 '18 at 12:45
Yes, a using block would have been the better practice. Although I don't think this Timer really needs it, it's more a formality form its base class. And we are at the end of Main anyway. – bommelding Oct 08 '18 at 12:53

Dmitry Bychenko · Answer 2 · 2018-10-08T12:26:52.060

1

When checking for == you actually compare ticks: if

 DateTime.Now == 2018-10-18 13:19:50.0000000

and thus there's only a tiny probability to go off Beep:

 ...
 DateTime.Now == 2018-10-18 13:19:49.9999852
 DateTime.Now == 2018-10-18 13:19:49.9999989 // Transition: no beep here
 DateTime.Now == 2018-10-18 13:19:50.0000007 // infinte loop from now on
 ...

Try different test (quick patch; Timer is a better solution):

    var xx = new DateTime(2018,10,8,13,19,50);

    while (true)
    {
        // If DateTime.Now exceeds xx 
        if (DateTime.Now >= xx) {
            // bee..eep
            Console.Beep();

            // and break the loop  
            break;
        }
    }

edited Oct 08 '18 at 12:26

answered Oct 08 '18 at 12:24

Dmitry Bychenko

180,369
20
160
215

3

Worth mentioning that this code should be periodically run by a timer rather than a `while` loop too, unless the objective is to indirectly heat their workspace. – Damien_The_Unbeliever Oct 08 '18 at 12:26
i guess that solves my issue i'll use a timer next time thanks a lot – crystals Oct 08 '18 at 12:28
@TimSchmelter i just tried to do this with a datetime justt to see if it was possible it isn't part of an app – crystals Oct 08 '18 at 12:31

score 0 · Answer 3 · answered Oct 08 '18 at 12:30

Time can be divided into really, really small fractions. You need to decide the resolution of time you're okay with. Should it beep if it is the same time down to the second? Or should it be the same time down to the millisecond? Or the nanosecond?

Once you've decided on this, you need to declare your xx value down to that precision, and in the loop, truncate DateTime.Now to the required precision. Then your comparison will do what you want.

score 0 · Answer 4 · answered Oct 08 '18 at 12:31

There are many approaches.

You could use the task scheduler Creating Scheduled Tasks
or could use Quartz.Net Cron with Quartz
or just make a sleep:

var xx = new DateTime(2018,10,8,13,19,50);

System.Threading.Thread.Sleep(new TimeSpan(xx - DateTime.Now).TotalMilliseconds);

Console.Beep();

C# check if Datetime.now is a specific time

4 Answers4