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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CLOCK(3P) POSIX Programmer's Manual CLOCK(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
clock — report CPU time used
#include <time.h>
clock_t clock(void);
The functionality described on this reference page is aligned
with the ISO C standard. Any conflict between the requirements
described here and the ISO C standard is unintentional. This
volume of POSIX.1‐2017 defers to the ISO C standard.
The clock() function shall return the implementation's best
approximation to the processor time used by the process since the
beginning of an implementation-defined era related only to the
process invocation.
To determine the time in seconds, the value returned by clock()
should be divided by the value of the macro CLOCKS_PER_SEC.
CLOCKS_PER_SEC is defined to be one million in <time.h>. If the
processor time used is not available or its value cannot be
represented, the function shall return the value (clock_t)-1.
No errors are defined.
The following sections are informative.
None.
In programming environments where clock_t is a 32-bit integer
type and CLOCKS_PER_SEC is one million, clock() will start
failing in less than 36 minutes of processor time for signed
clock_t, or 72 minutes for unsigned clock_t. Applications
intended to be portable to such environments should use times()
instead (or clock_gettime() with CLOCK_PROCESS_CPUTIME_ID, if
supported).
In order to measure the time spent in a program, clock() should
be called at the start of the program and its return value
subtracted from the value returned by subsequent calls. The value
returned by clock() is defined for compatibility across systems
that have clocks with different resolutions. The resolution on
any particular system need not be to microsecond accuracy.
None.
None.
asctime(3p), clock_getres(3p), ctime(3p), difftime(3p),
gmtime(3p), localtime(3p), mktime(3p), strftime(3p),
strptime(3p), time(3p), times(3p), utime(3p)
The Base Definitions volume of POSIX.1‐2017, time.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 CLOCK(3P)
Pages that refer to this page: time.h(0p), asctime(3p), ctime(3p), difftime(3p), gmtime(3p), localtime(3p), mktime(3p), strftime(3p), time(3p)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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