clock_t clock() ambiguity

[Matt]

Does clock_t clock() measure real time or process time? Unless I have
missed something, Stroustrup's treatment in TC++PL (section D.4.4.1) is
none too clear on that question.

Is clock() well-implemented for the major compilers g++, VC++, and
Macintosh compilers and other C++ compilers on Linux/Unix, Windows, and
MacOS?

[Ian Collins]

Phlip wrote:

Default User wrote:

>>"The clock function tells how much time the calling process has used."

It is not the wall time, it's the process time.

Despite, uh, saying "wall" time at the top of the page?

Please Google [wall-clock time]. If it's meaning isn't related to the
movement of a clock's hands while the program runs, then I'm wrong.
Otherwise, the MSDN page is inconsistent with itself.

A Win32 test involving Sleep() and two clock() calls would instantly answer
questions about the actual implementation.

And please be more careful with your own claims.

Brian's claim is correct.

From C99 7.23.2.1:

The clock function returns the implementation' s best approximation to
the processor time used by the program since the beginning of an
implementation-defined era related only to the program invocation.

--
Ian Collins.

[Matt]

Phlip wrote:

Matt wrote:

>>Does clock_t clock() measure real time or process time? Unless I have
missed something, Stroustrup's treatment in TC++PL (section D.4.4.1) is
none too clear on that question.

Is clock() well-implemented for the major compilers g++, VC++, and
Macintosh compilers and other C++ compilers on Linux/Unix, Windows, and
MacOS?

http://msdn.microsoft.com/library/de..._crt_clock.asp

Note the compatibility is "ANSI", which is MS's code for the "ISO C
Standard". All compilers worth using will have it.

Then note the first line is "Calculates the wall-clock time used by the
calling process." That "wall-clock" is jargon for real time, not process
time. And "used by the calling process" means the "epoch" starts when the
program starts.

In future, please hit a question with Google before posting it! I answered
all your questions with the first citation for [msdn clock_t].

Thanks for your answers to all my two questions!

Your answer to my first question was wrong.

Your answer to my second question was nonexistent.

[Victor Bazarov]

Matt wrote:

Phlip wrote:

>Matt wrote:

>>Does clock_t clock() measure real time or process time? Unless I
have missed something, Stroustrup's treatment in TC++PL (section
D.4.4.1) is none too clear on that question.

Is clock() well-implemented for the major compilers g++, VC++, and
Macintosh compilers and other C++ compilers on Linux/Unix, Windows,
and MacOS?

http://msdn.microsoft.com/library/de..._crt_clock.asp

Note the compatibility is "ANSI", which is MS's code for the "ISO C
Standard". All compilers worth using will have it.

Then note the first line is "Calculates the wall-clock time used by
the calling process." That "wall-clock" is jargon for real time, not
process time. And "used by the calling process" means the "epoch"
starts when the program starts.

In future, please hit a question with Google before posting it! I
answered all your questions with the first citation for [msdn
clock_t].

Thanks for your answers to all my two questions!

Your answer to my first question was wrong.

In what way was it "wrong"? You asked "real time or process time"? The
answer was 'wall-clock' and the explanation given that it is "real time
not process time". How in hell is it "wrong"?

Your answer to my second question was nonexistent.

The asnwer to your second question was "All complers worth using will have
it". To me it means "implemente d". As to "well" or "not well", we cannot
tell -- it's implementation-specific and we don't discuss implementations .
Most compilers have their own newsgroups, consider posting there. Also,
if you need information on "other compilers for <blahplatform ", please
consider asking in the newsgroup[s] dedicated to the platform[s].

Also, complaining about free advice is non-sensical. You asked a question,
you received _a_ response. Take it or leave it, don't bitch about it.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[peter koch]

Matt wrote:

Does clock_t clock() measure real time or process time?

[snip]

To add to the confusion, I have just tested a program using clock() on
Solaris and Windows NT. On both platforms clock() did seem to give
wall-clock (that is elapsed) time - the same result as is available
with gettickcount() on windows and time() on Solaris.
To get processor time, I had to use GetProcessInfo on Windows and
getrusage on Solaris (not 100% confident on those last names - i do not
have the code present).

/Peter

[Phlip]

peter koch wrote:

Matt wrote:

>Does clock_t clock() measure real time or process time?

To add to the confusion, I have just tested a program using clock() on
Solaris and Windows NT. On both platforms clock() did seem to give
wall-clock (that is elapsed) time - the same result as is available
with gettickcount() on windows and time() on Solaris.
To get processor time, I had to use GetProcessInfo on Windows and
getrusage on Solaris (not 100% confident on those last names - i do not
have the code present).

Did your test use a Sleep(big number)? Sleep's documentation claims it
suspends the CPU activity for a process...

--
Phlip
http://c2.com/cgi/wiki?ZeekLand <-- NOT a blog!!!

[peter koch]

Phlip wrote:

peter koch wrote:

Matt wrote:

Does clock_t clock() measure real time or process time?

To add to the confusion, I have just tested a program using clock() on
Solaris and Windows NT. On both platforms clock() did seem to give
wall-clock (that is elapsed) time - the same result as is available
with gettickcount() on windows and time() on Solaris.
To get processor time, I had to use GetProcessInfo on Windows and
getrusage on Solaris (not 100% confident on those last names - i do not
have the code present).

Did your test use a Sleep(big number)? Sleep's documentation claims it
suspends the CPU activity for a process...

Yes. I did measure a few busy loops (calculating e.g. sin() repeatedly)
and one sleep for app. six seconds. The results were consistent: clock
gave same result as gettickcount on windows, whereas GetProcessInfo
gave the same results on the busy loops and 0 when calling Sleep.

/Peter

>
--
Phlip
http://c2.com/cgi/wiki?ZeekLand <-- NOT a blog!!!

[Phlip]

peter koch wrote:

Yes. I did measure a few busy loops (calculating e.g. sin() repeatedly)
and one sleep for app. six seconds. The results were consistent: clock
gave same result as gettickcount on windows, whereas GetProcessInfo
gave the same results on the busy loops and 0 when calling Sleep.

Thanks. You have restored my faith in MSDN.

--
Phlip
http://c2.com/cgi/wiki?ZeekLand <-- NOT a blog!!!

[mlimber]

Default User wrote:

mlimber wrote:

Matt wrote:

Does clock_t clock() measure real time or process time? Unless I
have missed something, Stroustrup's treatment in TC++PL (section
D.4.4.1) is none too clear on that question.

IIRC, it's not defined by the C or C++ standards.

From the C99 draft standard:

[snip]

Apparently, IIRC = I didn't recall correctly. ;-)

Cheers! --M

[peter koch]

Phlip wrote:

peter koch wrote:

Yes. I did measure a few busy loops (calculating e.g. sin() repeatedly)
and one sleep for app. six seconds. The results were consistent: clock
gave same result as gettickcount on windows, whereas GetProcessInfo
gave the same results on the busy loops and 0 when calling Sleep.

Thanks. You have restored my faith in MSDN.

>From the other posts it seems to me that Windows NT as well as Solaris

got it wrong. This also explains my collegues surprise when I told them
that clock() returns elapsed time - they thought that clock() returned
processortime.
Could it be that Solaris and Windows NT shares a flawed codebase from
some time in the distant past?

/Peter

--
Phlip
http://c2.com/cgi/wiki?ZeekLand <-- NOT a blog!!!

[Default User]

Phlip wrote:

peter koch wrote:

Yes. I did measure a few busy loops (calculating e.g. sin()
repeatedly) and one sleep for app. six seconds. The results were
consistent: clock gave same result as gettickcount on windows,
whereas GetProcessInfo gave the same results on the busy loops and
0 when calling Sleep.

Thanks. You have restored my faith in MSDN.

I'm not sure what faith. The documentation is either inconsistent,
confusing, or just wrong.

This whole conversation seemed somewhat familiar, a bit of Groupling
came up with this:

<http://groups.google.com/group/comp....hread/fb0f9076
19ac71fe/7a52324dcae9a6f d>
Victor said then that Microsoft screwed up the implementation of
clock() in Visual Studio, and my little experiment seemed to confirm
that.

Brian