Allan Bruce wrote:
"Richard Bos" <rl*@hoekstra-uitgeverij.nl> wrote in message
news:3f*****************@news.nl.net... "Allan Bruce" <al*****@TAKEAWAYf2s.com> wrote:
"Terry Andersen" <te**@sea.com> wrote in message
news:bg**********@news.net.uni-c.dk...
> Can I operate on milliseconds in C? Is there a standard library where I > could retreive the system time in a better resolution than seconds.....? > The time_t gives me only the time like 12:32:11.........
> Any ideas.....?
have a look at clock()
I think its part of the standard for millisecond resolution
Not even close. clock() returns the processor time used by the program,
not the current clock time;
You are correct, it has nothing to do with the system time at all.
moreover, you have no guarantee whatsoever
about the precision of its return value.
Is this strictly true? The time.h header also specifies CLOCKS_PER_SEC which
one can use in order to find out the time in seconds. If CLOCKS_PER_SEC is
1000 then we know that the resolution is microsecond.
You mean "millisecond," but it doesn't really matter:
CLOCKS_PER_SEC tells us the units in which `clock_t' expresses
its value, but not the accuracy with which that value is
measured.
("Huh?")
One light-year is the distance a photon travels in one
year in an undisturbed vacuum. The "units" program available
on many Unix systems tells me that this distance is 9.460528e+15
meters. Does that mean that the length of the light-year is
known to an accuracy of plus-or-minus half a meter? Of course
not: it just means that the meter is one of the standard units
in which length is expressed.
On the system I'm using at the moment, CLOCKS_PER_SEC is
one million, meaning that `clock_t' values are expressed to
a precision of one microsecond. But the underlying hardware
clock ticks at 100Hz, so clock() cannot actually measure an
interval shorter than ten milliseconds.
Thought experiment: Express your age as a `clock_t' value
(ignoring possible overflow), using CLOCKS_PER_SEC as it's
defined on your favorite platform. Do you believe the answer?
Precision is one thing, accuracy is another.
--
Er*********@sun.com