clock(S)                       6 January 1993                       clock(S)


 Name

    clock - report CPU time used

 Syntax


    cc  . . .  -lc


    long clock ()


 Description

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

    The resolution of the clock is 10 milliseconds.

 Notes

    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 wraps around after accumulating only 2147
    seconds of CPU time (about 36 minutes).

    The frequency of the system clock in ticks per second can be set via the
    environment variable HZ.  clock uses gethz(S), which in turn uses HZ, in
    calculating the return value.  If this fails, the default value, set in
    <sys/param.h>, is used instead and a warning message is printed to
    stderr.

 See also

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

 Standards conformance

    clock is conformant with:
    AT&T SVID Issue 2;
    and X/Open Portability Guide, Issue 3, 1989.