ceph/src/boost/libs/chrono/doc/stopwatches/motivation.qbk

   1 [/
   2  / Copyright (c) 2009-20012 Vicente J. Botet Escriba
   3  /
   4  / Distributed under the Boost Software License, Version 1.0. (See accompanying
   5  / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6  /]
   7
   8
   9 [/==================]
  10 [/section Motivation]
  11 [/==================]
  12
  13
  14 [heading Measuring elapsed time]
  15
  16 Knowing how long a program, a function or a specific code block takes to execute is useful in both test and production environments.
  17 __Boost_Chrono introduces the __strict_stopwatch_concept concept which is a mechanism to measure the elapsed time.
  18 __strict_stopwatch`<>` is the basic model of __strict_stopwatch_concept.
  19
  20 [heading Reporting elapsed time]
  21
  22 It is often necessary to report elapsed time on a user display or in a log file.  __stopwatch_reporter provides a runtime reporting mechanism for this purpose which can be invoked in just one line of code.
  23
  24     using namespace boost::chrono;
  25     int main()
  26     {
  27         __stopwatch_reporter<__stopwatch<__process_cpu_clocks> > _;
  28       // ...
  29     }
  30
  31 Will produce the following output
  32
  33     real 0.034s, cpu 0.031s (93.0%), user 0.031s, system 0.000s
  34
  35 As this is one of the expression more commonly use, the library provides a __stopclock shortcut so the preceding can be written as
  36
  37     int main()
  38     {
  39         __stopclock<__process_cpu_clocks> _;
  40       // ...
  41     }
  42
  43