NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/13432

Internet Message Format | 1996-08-05 | 2.7 KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: delays: creating time delays with time.h (unix c)
Date: Sat, 06 Apr 96 22:03:19 GMT
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In article <Pine.SUN.3.92.960404210632.28756A-100000@suntan>
           [e-mail] "CS" writes:

>Hello! I'm trying to figure out if I can use the standard library (time.h)
>to create a delay function where the program will pause for x amount of
>time before continuing. 'x' I need it to be a value representing either
>10th of a second or 100th of a second.

The only functions the standard library gives you to read time values are
time() and clock(). You get no guarantees as to their granularity, however.
In many systems time() has a granularity of 1 second so doesn't fit
your criteria. clock() doesn't measure wall-clock time but rather CPU time
used. On a system without multi-tasking this may amount to the same thing
but isn't in general.

>Please, no references to using non-standard libraries: this code has to be
>as platform independent as possible.

I think you'll just have to accept that there is no single portable function
that meets your requirements. I suggest you create your own delay function
and use conditional compilation to compile code in it that is appropriate to
the system e.g. using clock, nap, usleep, select, poll etc. as appropriate.
One thing you definitely don't want to do is busy-wait on a multi-tasking
system.

>On that same note, suppose I have a variable getting the value from the
>clock() function... how do I print the variable (of type clock_t or
>time_t)? Thanks for your help!

A clock_t value doesn't mean much by itself, the only quantity that has
meaning is the difference between two such values. You can print the difference
in seconds out using something like:

     clock_t start, end;

     start = clock();

     ...

     end = clock();

     printf("%Lf\n", ((long double)end - start) / CLOCKS_PER_SEC);

For time_t there are various function to print it out formatted dates and
times, e.g. ctime, gmtime, localtime, asctime, strftime. You can also use
difftime to get the difference in seconds between 2 time_t values. The
representation of time_t itself is unspecified so printing it out directly
doesn't guarantee anything meaningful.

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
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