Timers in c

This is a discussion on Timers in c within the C Programming forums, part of the General Programming Boards category; I wanted to know if theres any timers in C linux programming and if anyone could give an example. So ...

  1. #1
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    Timers in c

    I wanted to know if theres any timers in C linux programming and if anyone could give an example. So I don't want something like sleep(). Because I want the timer in an if statement since the statement will be in an infinite while loop. That onces the timer goes off then the program will process the code in the if statement. Is there anything like that in C linux.

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    So look in <time.h> for the standard stuff, and maybe unistd.h if you want something Linux specific, for getting the current time. (Presumably you'd get the time when you start the clock and then use something like difftime to get the current reading of the clock.)

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    So I looked it up and It doesnt really seem to get any data types towards teh milisecond acting as a stop watch kind of. Is the only method have two timers and getting the differences until it matches up with the desired time?

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    MTK
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    Code:
    man gettimeofday
    man ftime
    Last edited by MTK; 09-09-2009 at 11:54 AM.

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    Quote Originally Posted by kiros88 View Post
    So I looked it up and It doesnt really seem to get any data types towards teh milisecond acting as a stop watch kind of. Is the only method have two timers and getting the differences until it matches up with the desired time?
    Are you thinking of something like sleep(in seconds), or delay(in milliseconds) ?

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    You can use the alarm() or ualarm() function to trigger an event after the specified number of seconds / microseconds have elapsed. Trap the SIGALRM signal by writing a signal handler and put the if-else statement inside it.

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    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    . . . then there is always nanosleep()

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    spurious conceit MK27's Avatar
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    Quote Originally Posted by kiros88 View Post
    Is the only method have two timers and getting the differences until it matches up with the desired time?
    That is why they call it "low level programming"

    Since you are using linux, you can use Glib. Take a look here:

    Timers

    (Ignore the fact that this is presented as part of the GNOME documentation, it does not require or depend on GNOME)

    Then take a look here

    The Main Event Loop

    and search for "g_timeout_add". This allows you to set a callback to occur at a certain time, IF you are using the Glib "main event loop".

    Which is a lot to swallow all at once, but Glib has TONS of functionality build into it -- complex datatypes like linked lists and hash tables, "g" threads, IO channels, on and on, it's a kind of whahoo! shopping spree library and if you intend to program for linux worth the time.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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    I don't want to sleep or delay the program because i want the rest of the code to be runnning since im planning to just use the timer for and if else statement. I was looking for alarm() but what header file uses it

  10. #10
    MTK
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    So you want it like a stopwatch?

    Why not just save the start time and trigger when the difference is right?

  11. #11
    Frequently Quite Prolix dwks's Avatar
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    If you want to know how alarm() works, type the command "man alarm".
    dwk

    Seek and ye shall find. quaere et invenies.

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    Captain Crash brewbuck's Avatar
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    alarm() is limited to an integer number of seconds for the delay. These days it is more common to use setitimer() instead which allows for sub-second delays.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Does anyone have a really simple example of setitimer I'm looking online and I found one but its kinda of confusing to understand
    Code:
    #include <stdio.h>
    #include <signal.h>
    #include <sys/time.h>
    
    #define INTERVAL 5
    
    int howmany = 0;
    void alarm_wakeup (int i)
    {
       struct itimerval tout_val;
       signal(SIGALRM,alarm_wakeup);
       howmany += INTERVAL;
       printf("\n%d sec up partner, Wakeup!!!\n",howmany);
       tout_val.it_interval.tv_sec = 0;
       tout_val.it_interval.tv_usec = 0;
       tout_val.it_value.tv_sec = INTERVAL; /* 10 seconds timer */
       tout_val.it_value.tv_usec = 0;
       setitimer(ITIMER_REAL, &tout_val,0);
    }
    
    void exit_func (int i)
    {
        signal(SIGINT,exit_func);
        printf("\nBye Bye!!!\n");
        exit(0);
    }
    
    int main ()
    {
      struct itimerval tout_val;
     
      tout_val.it_interval.tv_sec = 0;
      tout_val.it_interval.tv_usec = 0;
      tout_val.it_value.tv_sec = INTERVAL; /* 10 seconds timer */
      tout_val.it_value.tv_usec = 0;
      setitimer(ITIMER_REAL, &tout_val,0);
    
      signal(SIGALRM,alarm_wakeup); /* set the Alarm signal capture */
      signal(SIGINT,exit_func);
      
      while (1)
      {
        //printf("!");
      } 
      return 0;
    }
    I dont really understand what calls the exit signal

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    Perhaps start off with the simpler alarm() interface before moving to setitimer(). If you want to set a timer in milliseconds then consider using the microseconds analog of alarm() ie ualarm().

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