delay loop output in C++

Question

I have a while loop that runs in a do while loop. I need the while loop to run exactly every second no faster no slower. but i'm not sure how i would do that. this is the loop, off in its own function. I have heard of the sleep() function but I also have heard that it is not very accurate.

int min5()
{
    int second = 00;
    int minute = 0;
    const int ZERO = 00;

    do{
        while (second <= 59){
        if(minute == 5) break;
        second += 1;
        if(second == 60) minute += 1;
        if(second == 60) second = ZERO;
        if(second < 60) cout << "Current Time> "<< minute <<" : "<< second <<" \n";
        }
      } while (minute <= 5);
}

Answer 1

Sleep(1000);

http://msdn.microsoft.com/en-us/library/ms686298(VS.85).aspx

Answer 2

The best accuracy you can achieve is by using Operating System (OS) functions. You need to find the API that also has a callback function. The callback function is a function you write that the OS will call when the timer has expired.

Be aware that the OS may lose timing precision due to other tasks and activities that are running while your program is executing.

Answer 3

In Windows for example, there is a possibility to create a waitable timer object.

If that's Your operating system check the documentation here for example Waitable Timer Objects.

From the code You presented it looks like what You are trying to do can be done much easier with sleep. It doesn't make sense to guarantee that Your loop body is executed exactly every 1 second. Instead make it execute 10 times a second and check if the time that elapsed form the last time, You took some action, is more than a second or not. If not, do nothing. If yes, take action (print Your message, increment variables etc), store the time of last action and loop again.

Answer 4

As someone else posted, your OS may provide some kind of alarm or timer functionality. You should try to use this kind of thing rather than coding your own polling loop. Polling the time means you need to be context switched in every second, which keeps your code running when the system could be doing other stuff. In this case you interrupt someone else 300 times just to say "are we done yet".

Also, you should never make assumptions about the duration of a sleep - even if you had a real time OS this would be unsafe - you should always ask the real time clock or tick counter how much time has elapsed each time because otherwise any errors accumulate so you will get less and less accurate over time. This is true even on a real time system because even if a real time system could sleep accurately for 1 second, it takes some time for your code to run so this timing error would accumulate on each pass through the loop.

Answer 5

If you want a portable solution, you shouldn't expect high-precision timing. Usually, you only get that with a platform-dependent solution.

A portable (albeit not very CPU-efficient, nor particularly elegant) solution might make use of a function similar to this:

#include <ctime>

void wait_until_next_second()
{
    time_t before = time(0);
    while (difftime(time(0), before) < 1);
}

You'd then use this in your function like this:

int min5()
{
    wait_until_next_second();  // synchronization (optional), so that the first
                               // subsequent call will not take less than 1 sec.
    ...
    do
    {
        wait_until_next_second();  // waits approx. one second
        while (...)
        {
            ...
        }
    } while (...)
}

---

Some further comments on your code:

• Your code gets into an endless loop once minute reaches the value 5.

• Are you aware that 00 denotes an octal (radix 8) number (due to the leading zero)? It doesn't matter in this case, but be careful with numbers such as 017. This is decimal 15, not 17!

• You could incorporate the seconds++ right into the while loop's condition: while (seconds++ <= 59) ...

• I think in this case, it would be better to insert endl into the cout stream, since that will flush it, while inserting "\n" won't flush the stream. It doesn't truly matter here, but your intent seems to be to always see the current time on cout; if you don't flush the stream, you're not actually guaranteed to see the time message immediately.