CLOCK(P) POSIX Programmer's Manual CLOCK(P)NAMEclock - report CPU time used
SYNOPSIS
#include <time.h>
clock_t clock(void);
DESCRIPTION
The clock() function shall return the implementation's best approxima‐
tion 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 dif‐
ferent 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 ALSOasctime() , ctime() , difftime() , gmtime() , localtime() , mktime() ,
strftime() , strptime() , time() , utime() , the Base Definitions vol‐
ume 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 Technology
-- 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(P)
