Man

Command Section
CLOCK(3)               FreeBSD Library Functions Manual               CLOCK(3)

NAME
     clock - determine processor time used

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <time.h>

     clock_t
     clock(void);

DESCRIPTION
     The clock() function determines the amount of processor time used since
     the invocation of the calling process, measured in CLOCKS_PER_SECs of a
     second.

RETURN VALUES
     The clock() function returns the amount of time used unless an error
     occurs, in which case the return value is -1.

SEE ALSO
     getrusage(2), clocks(7)

STANDARDS
     The clock() function conforms to ISO/IEC 9899:1990 (``ISO C90'').
     However, Version 2 of the Single UNIX Specification (``SUSv2'') requires
     CLOCKS_PER_SEC to be defined as one million.  FreeBSD does not conform to
     this requirement; changing the value would introduce binary
     incompatibility and one million is still inadequate on modern processors.

FreeBSD 11.1-RELEASE-p4          June 4, 1993          FreeBSD 11.1-RELEASE-p4
Command Section