clock − determine processor time



The function returns an approximation of processor time used
by the program.

The value returned is the CPU time used so far as a to get
the number of seconds used, divide by If the processor time
used is not available or its value cannot be represented,
the function returns the value

For an explanation of the terms used in this section, see

│Interface Attribute     Value   │
│          │ Thread safety MT‐Safe │

POSIX.1‐2001, POSIX.1‐2008, C89, C99.  XSI requires that
CLOCKS_PER_SEC equals 1000000 independent of the actual

The C standard allows for arbitrary values at the start of
the program; subtract the value returned from a call to at
the start of the program to get maximum portability.

     Note that the time can wrap around.  On a 32‐bit system
where CLOCKS_PER_SEC equals 1000000 this function will
return the same value approximately every 72 minutes.

     On several other implementations, the value returned by
also includes the times of any children whose status has
been collected via (or another wait‐type call).  Linux does
not include the times of waited‐for children in the value
returned by The function, which explicitly returns
(separate) information about the caller and its children,
may be preferable.

     In glibc 2.17 and earlier, was implemented on top of
For improved accuracy, since glibc 2.18, it is implemented
on top of (using the clock).

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