Manual Pages  — CLOCK

clock – determine processor time used

LIBRARY SYNOPSIS DESCRIPTION RETURN VALUES SEE ALSO STANDARDS

Standard C Library (libc, -lc)

#include <time.h>

clock_t
clock(void);

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.

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

The clock() function conforms to ISO/IEC 9899:1990 ("ISO C90"). However, Version 2 of the Single UNIX Specification 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.