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libs/math/example/lexical_cast_native.cpp

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+/** lexical_cast_nonfinite_facets.cpp
+*
+* Copyright (c) 2011 Paul A. Bristow
+*
+* Distributed under the Boost Software License, Version 1.0.
+* (See accompanying file LICENSE_1_0.txt
+* or copy at http://www.boost.org/LICENSE_1_0.txt)
+*
+* This very simple program illustrates how to use the
+* `boost/math/nonfinite_num_facets.hpp' with lexical cast
+* to obtain C99 representation of infinity and NaN.
+* This example is from the original Floating Point  Utilities contribution by Johan Rade.
+* Floating Point Utility library has been accepted into Boost,
+* but the utilities are incorporated into Boost.Math library.
+*
+\file
+
+\brief A very simple example of using lexical cast with
+non_finite_num facet for C99 standard output of infinity and NaN.
+
+\detail This example shows how to create a C99 non-finite locale,
+and imbue input and output streams with the non_finite_num put and get facets.
+This allows lexical_cast output and input of infinity and NaN in a Standard portable way,
+This permits 'loop-back' of output back into input (and portably across different system too).
+
+*/
+
+#include <boost/math/special_functions/nonfinite_num_facets.hpp>
+using boost::math::nonfinite_num_get;
+using boost::math::nonfinite_num_put;
+
+#include <boost/lexical_cast.hpp>
+using boost::lexical_cast;
+
+#include <iostream>
+using std::cout;
+using std::endl;
+using std::cerr;
+
+#include <iomanip>
+using std::setw;
+using std::left;
+using std::right;
+using std::internal;
+
+#include <string>
+using std::string;
+
+#include <sstream>
+using std::istringstream;
+
+#include <limits>
+using std::numeric_limits;
+
+#include <locale>
+using std::locale;
+
+#include <boost/assert.hpp>
+
+int main ()
+{
+  std::cout << "lexical_cast example (NOT using finite_num_facet)." << std::endl;
+    
+  if((std::numeric_limits<double>::has_infinity == false) || (std::numeric_limits<double>::infinity() == 0))
+  {
+    std::cout << "Infinity not supported on this platform." << std::endl;
+    return 0;
+  }
+
+  if((std::numeric_limits<double>::has_quiet_NaN == false) || (std::numeric_limits<double>::quiet_NaN() == 0))
+  {
+    std::cout << "NaN not supported on this platform." << std::endl;
+    return 0;
+  }
+  
+  // Some tests that are expected to fail on some platforms.
+  // (But these tests are expected to pass using non_finite num_put and num_get facets).
+
+  // Use the current 'native' default locale.
+  std::locale default_locale (std::locale::classic ()); // Note the currrent (default C) locale.
+
+  // Create plus and minus infinity.
+  double plus_infinity = +std::numeric_limits<double>::infinity();
+  double minus_infinity = -std::numeric_limits<double>::infinity();
+
+  // and create a NaN (NotANumber).
+  double NaN = +std::numeric_limits<double>::quiet_NaN ();
+
+  // Output the nonfinite values using the current (default C) locale.
+  // The default representations differ from system to system,
+  // for example, using Microsoft compilers, 1.#INF, -1.#INF, and 1.#QNAN.
+  cout << "Using default locale" << endl;
+  cout << "+std::numeric_limits<double>::infinity() = " << plus_infinity << endl;
+  cout << "-std::numeric_limits<double>::infinity() = " << minus_infinity << endl;
+  cout << "+std::numeric_limits<double>::quiet_NaN () = " << NaN << endl;
+      
+  // Checks below are expected to fail on some platforms!
+
+  // Now try some 'round-tripping', 'reading' "inf"
+  double x = boost::lexical_cast<double>("inf");
+  // and check we get a floating-point infinity.
+  BOOST_ASSERT(x == std::numeric_limits<double>::infinity());
+
+  // Check we can convert the other way from floating-point infinity,
+  string s = boost::lexical_cast<string>(numeric_limits<double>::infinity());
+  // to a C99 string representation as "inf".
+  BOOST_ASSERT(s == "inf");
+
+  // Finally try full 'round-tripping' (in both directions):
+  BOOST_ASSERT(lexical_cast<double>(lexical_cast<string>(numeric_limits<double>::infinity()))
+    == numeric_limits<double>::infinity());
+  BOOST_ASSERT(lexical_cast<string>(lexical_cast<double>("inf")) == "inf");
+
+  return 0;
+} // int main()
+
+/*
+
+Output:
+
+from MSVC 10, fails (as expected)
+
+  lexical_cast_native.vcxproj -> J:\Cpp\fp_facet\fp_facet\Debug\lexical_cast_native.exe
+  lexical_cast example (NOT using finite_num_facet).
+  Using default locale
+  +std::numeric_limits<double>::infinity() = 1.#INF
+  -std::numeric_limits<double>::infinity() = -1.#INF
+  +std::numeric_limits<double>::quiet_NaN () = 1.#QNAN
+C:\Program Files\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppCommon.targets(183,5): error MSB3073: The command ""J:\Cpp\fp_facet\fp_facet\Debug\lexical_cast_native.exe"
+C:\Program Files\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppCommon.targets(183,5): error MSB3073: :VCEnd" exited with code 3.
+
+
+*/