ceph/src/boost/libs/math/example/lexical_cast_nonfinite_facets.cpp

   1 /** lexical_cast_nonfinite_facets.cpp
   2 *
   3 * Copyright (c) 2011 Paul A. Bristow
   4 *
   5 * Distributed under the Boost Software License, Version 1.0.
   6 * (See accompanying file LICENSE_1_0.txt
   7 * or copy at http://www.boost.org/LICENSE_1_0.txt)
   8 *
   9 * This very simple program illustrates how to use the
  10 * `boost/math/nonfinite_num_facets.hpp' with lexical cast
  11 * to obtain C99 representation of infinity and NaN.
  12 * This example is from the original Floating Point  Utilities contribution by Johan Rade.
  13 * Floating Point Utility library has been accepted into Boost,
  14 * but the utilities are incorporated into Boost.Math library.
  15 *
  16 \file
  17
  18 \brief A very simple example of using lexical cast with
  19 non_finite_num facet for C99 standard output of infinity and NaN.
  20
  21 \detail This example shows how to create a C99 non-finite locale,
  22 and imbue input and output streams with the non_finite_num put and get facets.
  23 This allows lexical_cast output and input of infinity and NaN in a Standard portable way,
  24 This permits 'loop-back' of output back into input (and portably across different system too).
  25
  26 See also lexical_cast_native.cpp which is expected to fail on many systems,
  27 but might succeed if the default locale num_put and num_get facets
  28 comply with C99 nonfinite input and output specification.
  29
  30 */
  31
  32 #include <boost/math/special_functions/nonfinite_num_facets.hpp>
  33 using boost::math::nonfinite_num_get;
  34 using boost::math::nonfinite_num_put;
  35
  36 #include <boost/lexical_cast.hpp>
  37 using boost::lexical_cast;
  38
  39 #include <iostream>
  40 using std::cout;
  41 using std::endl;
  42 using std::cerr;
  43
  44 #include <iomanip>
  45 using std::setw;
  46 using std::left;
  47 using std::right;
  48 using std::internal;
  49
  50 #include <string>
  51 using std::string;
  52
  53 #include <sstream>
  54 using std::istringstream;
  55
  56 #include <limits>
  57 using std::numeric_limits;
  58
  59 #include <locale>
  60 using std::locale;
  61
  62 #include <boost/assert.hpp>
  63
  64 int main ()
  65 {
  66   std::cout << "finite_num_facet with lexical_cast example." << std::endl;
  67
  68   // Example of using non_finite num_put and num_get facets with lexical_cast.
  69   //locale old_locale;
  70   //locale tmp_locale(old_locale, new nonfinite_num_put<char>);
  71   //// Create a new temporary output locale, and add the output nonfinite_num_put facet.
  72
  73   //locale new_locale(tmp_locale, new nonfinite_num_get<char>);
  74   // Create a new output locale (from the tmp locale), and add the input nonfinite_num_get facet.
  75
  76   // Note that you can only add facets one at a time,
  77   // unless you chain thus:
  78
  79   std::locale new_locale(std::locale(std::locale(),
  80     new boost::math::nonfinite_num_put<char>),
  81     new boost::math::nonfinite_num_get<char>);
  82
  83   locale::global(new_locale); // Newly constructed streams
  84   // (including those streams inside lexical_cast)
  85   // now use new_locale with nonfinite facets.
  86
  87   // Output using the new locale.
  88   cout << "Using C99_out_locale " << endl;
  89   cout.imbue(new_locale);
  90   // Necessary because cout already constructed using default C locale,
  91   // and default facets for nonfinites.
  92
  93     // Create plus and minus infinity.
  94   double plus_infinity = +std::numeric_limits<double>::infinity();
  95   double minus_infinity = -std::numeric_limits<double>::infinity();
  96
  97   // and create a NaN (NotANumber)
  98   double NaN = +std::numeric_limits<double>::quiet_NaN ();
  99   cout << "+std::numeric_limits<double>::infinity() = " << plus_infinity << endl;
 100   cout << "-std::numeric_limits<double>::infinity() = " << minus_infinity << endl;
 101   cout << "+std::numeric_limits<double>::quiet_NaN () = " << NaN << endl;
 102
 103   // Now try some 'round-tripping', 'reading' "inf".
 104   double x = boost::lexical_cast<double>("inf");
 105   // and check we get a floating-point infinity.
 106   BOOST_ASSERT(x == std::numeric_limits<double>::infinity());
 107   cout << "boost::lexical_cast<double>(\"inf\") = " << x << endl;
 108
 109   // Check we can convert the other way from floating-point infinity,
 110   string s = boost::lexical_cast<string>(numeric_limits<double>::infinity());
 111   // to a C99 string representation as "inf".
 112   BOOST_ASSERT(s == "inf");
 113
 114   // Finally try full 'round-tripping' (in both directions):
 115   BOOST_ASSERT(lexical_cast<double>(lexical_cast<string>(numeric_limits<double>::infinity()))
 116     == numeric_limits<double>::infinity());
 117   BOOST_ASSERT(lexical_cast<string>(lexical_cast<double>("inf")) == "inf");
 118
 119     return 0;
 120 } // int main()
 121
 122 /*
 123
 124 Output:
 125   finite_num_facet with lexical_cast example.
 126   Using C99_out_locale
 127   +std::numeric_limits<double>::infinity() = inf
 128   -std::numeric_limits<double>::infinity() = -inf
 129   +std::numeric_limits<double>::quiet_NaN () = nan
 130   boost::lexical_cast<double>("inf") = inf
 131
 132
 133 */