CLOCK
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
clock - determine processor time
SYNOPSIS
#include <time.h>
clock_t clock(void);
DESCRIPTION
The
clock()
function returns an approximation of processor time used by the program.
RETURN VALUE
The value returned is the CPU time used so far as a
clock_t;
to get the number of seconds used, divide by
CLOCKS_PER_SEC.
If the processor time used is not available or its value cannot
be represented, the function returns the value
(clock_t) -1.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
clock()
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99.
XSI requires that
CLOCKS_PER_SEC
equals 1000000 independent
of the actual resolution.
NOTES
The C standard allows for arbitrary values at the start of the program;
subtract the value returned from a call to
clock()
at the start of the program to get maximum portability.
Note that the time can wrap around.
On a 32-bit system where
CLOCKS_PER_SEC
equals 1000000 this function will return the same
value approximately every 72 minutes.
On several other implementations,
the value returned by
clock()
also includes the times of any children whose status has been
collected via
wait(2)
(or another wait-type call).
Linux does not include the times of waited-for children in the
value returned by
clock().
The
times(2)
function, which explicitly returns (separate) information about the
caller and its children, may be preferable.
In glibc 2.17 and earlier,
clock()
was implemented on top of
times(2).
For improved accuracy,
since glibc 2.18, it is implemented on top of
clock_gettime(2)
(using the
CLOCK_PROCESS_CPUTIME_ID
clock).
SEE ALSO
clock_gettime(2),
getrusage(2),
times(2)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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