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clock(3) [centos man page]

CLOCK(3)						     Linux Programmer's Manual							  CLOCK(3)

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. CONFORMING TO
C89, C99, POSIX.1-2001. POSIX 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. SEE ALSO
clock_gettime(2), getrusage(2), times(2) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
2008-08-28 CLOCK(3)

Check Out this Related Man Page

CLOCK(3P)						     POSIX Programmer's Manual							 CLOCK(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
clock - report CPU time used SYNOPSIS
#include <time.h> clock_t clock(void); DESCRIPTION
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. RETURN VALUE
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. ERRORS
No errors are defined. The following sections are informative. EXAMPLES
None. APPLICATION USAGE
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. The value returned by clock() may wrap around on some implementations. For example, on a machine with 32-bit values for clock_t, it wraps after 2147 seconds or 36 minutes. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
asctime(), ctime(), difftime(), gmtime(), localtime(), mktime(), strftime(), strptime(), time(), utime(), the Base Definitions volume of IEEE Std 1003.1-2001, <time.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 . IEEE
/The Open Group 2003 CLOCK(3P)

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