i swear i'm "special" somtimes.

This is a discussion on i swear i'm "special" somtimes. within the C++ Programming forums, part of the General Programming Boards category; what's the best way to get something to happen every say, 60 seconds? i've been trying with Code: if ((clock ...

  1. #1
    Registered User Terran's Avatar
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    i swear i'm "special" somtimes.

    what's the best way to get something to happen every say, 60 seconds? i've been trying with
    Code:
      if ((clock () /  CLOCKS_PER_SEC) % 60 == 0){
    from time.h but i'm not sure if that's the best way to do it.

  2. #2
    and the hat of int overfl Salem's Avatar
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    You're right, it isn't.

    clock() measures CPU time, not wall-clock time, so unless you're thrashing the CPU, that's gonna lag.
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  3. #3
    Registered User Terran's Avatar
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    Well i was trying to use
    Code:
    time_t  start, end;
    , and then something like
    Code:
     
    while(true) {
                    end = Not sure what to put here.
                    if ((end - start) ==0){
                             //do somthing
                    }
    }

  4. #4
    The larch
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    Look up difftime

    And you probably want to compare "now" (time(0)) with start to see if the difference is (greater or ?) equal to 60.0.
    I might be wrong.

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    Or if you want other applications to run whilst you are "waiting", use something like Sleep() [windows, 60000 will make 1 minute] or sleep() [Linux/Unix etc, 60 will make one minute].

    The OS will then take care of figuring out the time it needs to wake up again. It will be fairly precise, no less so than what you get if you spin in user-mode. The main difference is that if you spin in user-mode, the OS may think "CPU-intensive task", and put your task at a lower priority, whilst a "waiting" task will get raised priority. So it's likely to be MORE precise.

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  6. #6
    Registered User Terran's Avatar
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    ahh got it;

    Code:
        
    const int TimeElapse = 10; // amount of time to wait, in seconds.
    time_t now = time(0); // set the now time.
        while(true)
            if ((time(0)-now) % TimeElapse == 0) //comepare now to the current time, and modulus for zero.
                cout << time(0) << endl; // test std::cout
    obviously that's not exactly the code i'll use, but it shows that the if works.
    Last edited by Terran; 05-26-2008 at 05:23 PM.

  7. #7
    Algorithm Dissector iMalc's Avatar
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    You better hope nobody adjusts their computer clock whilst that code's running!
    Also, if there is a momentary delay such as when a page of virtual memory is loaded from the page file, then you could miss one of your periodic tasks.
    You must not look for a specific time. Instead, you'd wait until the time has been reached (or exceeded) and then remember that you have done the task for that minute and wait for the next one.

    The best way to do a periodic task really depends on the operating system (please state it).
    In a Windows app, using a timer to generate WM_TIMER messages is a good approach, for example.
    One could instead use GetTickCount() with code similiar to what you're posted, to avoid problems if your clock is changed.
    Last edited by iMalc; 05-27-2008 at 02:07 AM.
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  8. #8
    C++まいる!Cをこわせ!
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    I have a non CPU-eating function (that you could modify) that can be used to sleep or lock to a certain FPS, so to speak.
    Doing callbacks
    If you're interested.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
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    Title of your thread is a little too unobviously clear to me

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    If you really care about correctness, use difftime(). time_t is not guaranteed to be in seconds (although it almost always is).

    It is not considered very nice to perform "busy waiting", but like matsp pointed out, the way to perform a "sleep" is unfortunately (but understandibly) not standard across platforms.

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  11. #11
    Registered User Terran's Avatar
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    it's not like just eating time though. Say i want the user to still be able to use the menu functions while the program is still processing actions in the back and a certain action (say population of a planet) doubles every minute.

  12. #12
    C++まいる!Cをこわせ!
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    This calls for a threaded approach. One threads runs a message loop and blocks until messages are received and one thread performs all the other work you want.
    This will keep the interface smooth while you can still sleep/wait in the other thread.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  13. #13
    Registered User Terran's Avatar
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    guess i have to learn how to sew then!

  14. #14
    Algorithm Dissector iMalc's Avatar
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    We still don't know what OS yet.
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  15. #15
    Registered User Terran's Avatar
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    Oh, well Vista for the current sys i program on.

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