clock(S)

clock -- report CPU time used

Synopsis

   #include <time.h>
   
   clock_t clock(void);

Description

clock 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 system call, the pclose function, or the system function.

Dividing the value returned by clock by the constant CLOCKS_PER_SEC (or a million), defined in the time.h header file, will give the time in seconds.

The resolution of the clock is defined by CLK_TCK in limits.h, and is typically 1/100 or 1/60 of a second.

References

popen(S), system(S), times(S), wait(S)

Notices

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). If the process time used is not available or cannot be represented, clock returns the value (clock_t)-1.