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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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CLOCK(3) Linux Programmer's Manual CLOCK(3)
clock - determine processor time
#include <time.h>
clock_t clock(void);
The clock() function returns an approximation of processor time
used by the program.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│clock() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008, C89, C99. XSI requires that
CLOCKS_PER_SEC equals 1000000 independent of the actual
resolution.
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).
clock_gettime(2), getrusage(2), times(2)
This page is part of release 5.13 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/.
GNU 2021-03-22 CLOCK(3)
Pages that refer to this page: getrusage(2), times(2), ctime(3), system_data_types(7), time(7)
Copyright and license for this manual page
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