clock(3)                   Library Functions Manual                   clock(3)

NAME
       clock - determine processor time

LIBRARY
       Standard C library (libc, -lc)

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 |
       +--------------------------------------------+---------------+---------+
VERSIONS
       XSI requires that CLOCKS_PER_SEC equals 1000000 independent of the
       actual resolution.

       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.

STANDARDS
       C11, POSIX.1-2008.

HISTORY
       POSIX.1-2001, C89.

       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).

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.

SEE ALSO
       clock_gettime(2), getrusage(2), times(2)

Linux man-pages 6.7               2023-10-31                          clock(3)