ceph/src/boost/libs/spirit/doc/karma/num_list.qbk

   1 [/==============================================================================
   2     Copyright (C) 2001-2011 Hartmut Kaiser
   3     Copyright (C) 2001-2011 Joel de Guzman
   4
   5     Distributed under the Boost Software License, Version 1.0. (See accompanying
   6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7 ===============================================================================/]
   8
   9 [/////////////////////////////////////////////////////////////////////////////]
  10 [section:num_list Number List - Printing Numbers From a std::vector]
  11
  12 [heading Using the List Operator]
  13
  14 The C++ Standard library lacks an important feature, namely the support for
  15 any formatted output of containers. Sure, it's fairly easy to write a custom
  16 routine to output a specific container, but doing so over and over again is
  17 tedious at best. In this section we will demonstrate some more of the
  18 capabilities of __karma__ for generating output from arbitrary STL containers.
  19 We will build on the example presented in an earlier section (see
  20 [link spirit.karma.tutorials.warming_up Warming Up]).
  21
  22 The full source code of the example shown in this section can be found here:
  23 [@../../example/karma/num_list2.cpp num_list2.cpp].
  24
  25 [import ../../example/karma/num_list2.cpp]
  26
  27 This time we take advantage of Karma's __karma_list__ operator. The semantics
  28 of the list operator are fully equivalent to the semantics of the sequence
  29 we used before. The generator expression
  30
  31     double_ << *(',' << double_)
  32
  33 is semantically equivalent to the generator expression
  34
  35     double_ % ','
  36
  37 simplifying the overall code. The list operator's attribute is compatible with
  38 any STL container as well. For a change we use a `std::vector<double>`
  39 instead of the `std::list<double>` we used before. Additionally, the routine
  40 `generate_numbers` takes the container as a template parameter, so it will now
  41 work with any STL container holding `double` numbers.
  42
  43 [tutorial_karma_numlist2]
  44
  45 [note Despite the container being a template parameter, the __karma__
  46       formatting expression (`double_ % ','`) does not depend on the actual
  47       type of the passed container. The only precondition to be met here is
  48       that the elements stored in the container have to be convertible to
  49       `double`.]
  50
  51 [heading Generate Output from Arbitrary Data]
  52
  53 The output routine developed above is still not generically usable for all types
  54 of STL containers and for arbitrary elements stored in them. In order to be
  55 usable the items stored in the container still need to be convertible to a
  56 `double`. Fortunately __karma__ is capable to output arbitrary
  57 data types while using the same format description expression. It implements
  58 the [karma_stream `stream`] generators which are able to consume any attribute
  59 type as long as a matching standard streaming operator is defined. I.e.
  60 for any attribute type `Attrib` a function:
  61
  62     std::ostream& operator<< (std::ostream&, Attrib const&);
  63
  64 needs to be available. The [karma_stream `stream`] generator will use the
  65 standard streaming operator to generate the output.
  66
  67 The following example modifies the code shown above to utilize the
  68 [karma_stream `stream`] operator, which makes it compatible with almost any
  69 data type. We implement a custom data type `complex` to demonstrate this. The
  70 example shows how it is possible to integrate this (or any other) custom data
  71 type into the __karma__ generator framework.
  72
  73 [import ../../example/karma/num_list3.cpp]
  74
  75 This is the custom data structure together with the required standard streaming
  76 operator:
  77
  78 [tutorial_karma_numlist3_complex]
  79
  80 And this is the actual call to generate the output from a vector of those. This
  81 time we interleave the generated output with newline breaks (see
  82 __karma_eol__), putting each complex number onto a separate line:
  83
  84 [tutorial_karma_numlist3]
  85
  86 The code shown is fully generic and can be used with any STL container as long
  87 as the data items stored in that container implement the standard streaming
  88 operator.
  89
  90 The full source code of the example presented in this section can be found here:
  91 [@../../example/karma/num_list3.cpp num_list3.cpp].
  92
  93 [endsect]
  94
  95 [/////////////////////////////////////////////////////////////////////////////]
  96 [section:num_matrix Matrix of Numbers - Printing Numbers From a Matrix]
  97
  98 In this section we will discuss the possibilities of __karma__ when it comes to
  99 generating output from more complex - but still regular - data structures.
 100 For simplicity we will use a `std::vector<std::vector<int> >` as a poor
 101 man's matrix representation. But even if the data structure seems to be very
 102 simple, the presented principles are applicable to more complex, or custom
 103 data structures as well. The full source code of the example discussed in this
 104 section can be found here: [@../../example/karma/num_matrix.cpp num_matrix.cpp].
 105
 106 [import ../../example/karma/num_matrix.cpp]
 107
 108 [endsect]