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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).
- See also lexical_cast_native.cpp which is expected to fail on many systems,
- but might succeed if the default locale num_put and num_get facets
- comply with C99 nonfinite input and output specification.
- */
- #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 << "finite_num_facet with lexical_cast example." << std::endl;
- // Example of using non_finite num_put and num_get facets with lexical_cast.
- //locale old_locale;
- //locale tmp_locale(old_locale, new nonfinite_num_put<char>);
- //// Create a new temporary output locale, and add the output nonfinite_num_put facet.
- //locale new_locale(tmp_locale, new nonfinite_num_get<char>);
- // Create a new output locale (from the tmp locale), and add the input nonfinite_num_get facet.
- // Note that you can only add facets one at a time,
- // unless you chain thus:
-
- std::locale new_locale(std::locale(std::locale(),
- new boost::math::nonfinite_num_put<char>),
- new boost::math::nonfinite_num_get<char>);
-
- locale::global(new_locale); // Newly constructed streams
- // (including those streams inside lexical_cast)
- // now use new_locale with nonfinite facets.
- // Output using the new locale.
- cout << "Using C99_out_locale " << endl;
- cout.imbue(new_locale);
- // Necessary because cout already constructed using default C locale,
- // and default facets for nonfinites.
- // 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 ();
- 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;
- // 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());
- cout << "boost::lexical_cast<double>(\"inf\") = " << x << endl;
- // 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:
- finite_num_facet with lexical_cast example.
- Using C99_out_locale
- +std::numeric_limits<double>::infinity() = inf
- -std::numeric_limits<double>::infinity() = -inf
- +std::numeric_limits<double>::quiet_NaN () = nan
- boost::lexical_cast<double>("inf") = inf
- */
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