man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

clock(3C)

Name

clock - report CPU time used

Synopsis

#include <time.h>

clock_t clock(void);

Description

The clock() function returns the amount of CPU time (in microseconds) used since the first call to clock() in the calling process. The time reported is the sum of the user and system times of the calling process and its terminated child processes for which it has executed the wait(3C) function, the pclose(3C) function, or the system(3C) function.

Return Values

Dividing the value returned by clock() by the constant CLOCKS_PER_SEC, defined in the <time.h> header, will give the time in seconds. If the process time used is not available or cannot be represented, clock returns the value (clock_t) −1.

Usage

The value returned by clock() is defined in microseconds for compatibility with systems that have CPU clocks with much higher resolution. Because of this, the value returned will wrap around after accumulating only 2147 seconds of CPU time (about 36 minutes).

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
MT-Safe
Standard

See Also

times(2), popen(3C), system(3C), wait(3C), attributes(5), standards(5)