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