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(libc.info)CPU Time

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CPU Time Inquiry
----------------

   To get a process' CPU time, you can use the `clock' function.  This
facility is declared in the header file `time.h'.

   In typical usage, you call the `clock' function at the beginning and
end of the interval you want to time, subtract the values, and then
divide by `CLOCKS_PER_SEC' (the number of clock ticks per second) to
get processor time, like this:

     #include <time.h>
     
     clock_t start, end;
     double cpu_time_used;
     
     start = clock();
     ... /* Do the work. */
     end = clock();
     cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;

   Do not use a single CPU time as an amount of time; it doesn't work
that way.  Either do a subtraction as shown above or query processor
time directly.  Note: Processor Time.

   Different computers and operating systems vary wildly in how they
keep track of CPU time.  It's common for the internal processor clock
to have a resolution somewhere between a hundredth and millionth of a
second.

 - Macro: int CLOCKS_PER_SEC
     The value of this macro is the number of clock ticks per second
     measured by the `clock' function.  POSIX requires that this value
     be one million independent of the actual resolution.

 - Macro: int CLK_TCK
     This is an obsolete name for `CLOCKS_PER_SEC'.

 - Data Type: clock_t
     This is the type of the value returned by the `clock' function.
     Values of type `clock_t' are numbers of clock ticks.

 - Function: clock_t clock (void)
     This function returns the calling process' current CPU time.  If
     the CPU time is not available or cannot be represented, `clock'
     returns the value `(clock_t)(-1)'.