gettimeofday() vs. systime()

Kenny McCormack

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Jan 20, 2018, 11:03:01 AM1/20/18

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I was looking at the "time" extension lib (part of the gawk distro).

A couple questions about the gettimeofday() function arose:

1) Why this function? Isn't it the same as the built-in systime() function?
2) Except that it isn't quite the same. Observe:

$ gawk4 -l time 'BEGIN {print gettimeofday(), systime()}'
1.51646e+09 1516463840
$ gawk4 -l time 'BEGIN {printf("%20d%20d\n", gettimeofday(), systime())}'
1516463882 1516463882

Just curious. Why does it display in exponential notation the first time
(but systime() doesn't) ?

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Luuk

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Jan 20, 2018, 11:28:03 AM1/20/18

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On 20-01-18 17:02, Kenny McCormack wrote:
> I was looking at the "time" extension lib (part of the gawk distro).
>
> A couple questions about the gettimeofday() function arose:
>
> 1) Why this function? Isn't it the same as the built-in systime() function?
> 2) Except that it isn't quite the same. Observe:
>
> $ gawk4 -l time 'BEGIN {print gettimeofday(), systime()}'
> 1.51646e+09 1516463840
> $ gawk4 -l time 'BEGIN {printf("%20d%20d\n", gettimeofday(), systime())}'
> 1516463882 1516463882
>
> Just curious. Why does it display in exponential notation the first time
> (but systime() doesn't) ?
>

man gawk says:
systime() Return the current time of day as the number of seconds since
the Epoch

here is says:
gettimeofday() Return the time in seconds that has elapsed since
1970-01-01 UTC as a floating-point value.

Andrew Schorr

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Jan 20, 2018, 9:24:46 PM1/20/18

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On Saturday, January 20, 2018 at 11:03:01 AM UTC-5, Kenny McCormack wrote:
> 1) Why this function? Isn't it the same as the built-in systime() function?

It is not the same. The gettimeofday function has subsecond accuracy.

> 2) Except that it isn't quite the same. Observe:
>
> $ gawk4 -l time 'BEGIN {print gettimeofday(), systime()}'
> 1.51646e+09 1516463840
> $ gawk4 -l time 'BEGIN {printf("%20d%20d\n", gettimeofday(), systime())}'
> 1516463882 1516463882

Here's a better example:

bash-4.2$ gawk -l time 'BEGIN {printf "%.6f %.6f\n", systime(), gettimeofday(); sleep(.1); printf "%.6f %.6f\n", systime(), gettimeofday()}'
1516501463.000000 1516501463.549218
1516501463.000000 1516501463.649364

Regards,
Andy

Kenny McCormack

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Jan 21, 2018, 1:18:42 AM1/21/18

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In article <01600c56-0c5a-4d13...@googlegroups.com>,
Andrew Schorr <asc...@telemetry-investments.com> wrote:
...

>Here's a better example:
>
>bash-4.2$ gawk -l time 'BEGIN {printf "%.6f %.6f\n", systime(), gettimeofday();
>sleep(.1); printf "%.6f %.6f\n", systime(), gettimeofday()}'
>1516501463.000000 1516501463.549218
>1516501463.000000 1516501463.649364
>
>Regards,
>Andy

Interesting. Thanks!

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Andrew Schorr

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Jan 21, 2018, 9:55:34 PM1/21/18

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On Sunday, January 21, 2018 at 1:18:42 AM UTC-5, Kenny McCormack wrote:
> Interesting. Thanks!

And by the way, the man page does clearly state:

gettimeofday()
This function returns the number of seconds since the Epoch as a
floating-point value. It should have subsecond precision. It
returns -1 upon error and sets ERRNO to indicate the problem.

Regards,
Andy