Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

boost/lexical_cast.hpp

#ifndef BOOST_LEXICAL_CAST_INCLUDED
#define BOOST_LEXICAL_CAST_INCLUDED

// Boost lexical_cast.hpp header  -------------------------------------------//
//
// See http://www.boost.org for most recent version including documentation.
// See end of this header for rights and permissions.
//
// what:  lexical_cast custom keyword cast
// who:   contributed by Kevlin Henney,
//        enhanced with contributions from Terje Slettebø,
//        with additional fixes and suggestions from Gennaro Prota,
//        Beman Dawes, Dave Abrahams, Daryle Walker, Peter Dimov,
//        and other Boosters
// when:  November 2000, March 2003, June 2005

#include <cstddef>
#include <string>
#include <typeinfo>
#include <boost/config.hpp>
#include <boost/limits.hpp>
#include <boost/throw_exception.hpp>
#include <boost/type_traits/is_pointer.hpp>

#ifdef BOOST_NO_STRINGSTREAM
#include <strstream>
#else
#include <sstream>
#endif

#if defined(BOOST_NO_STRINGSTREAM) || \
    defined(BOOST_NO_STD_WSTRING) || \
    defined(BOOST_NO_STD_LOCALE) 
#define DISABLE_WIDE_CHAR_SUPPORT
#endif

namespace boost
{
    // exception used to indicate runtime lexical_cast failure
    class bad_lexical_cast : public std::bad_cast
    {
    public:
        bad_lexical_cast() :
        source(&typeid(void)), target(&typeid(void))
        {
        }
        bad_lexical_cast(
            const std::type_info &source_type,
            const std::type_info &target_type) :
            source(&source_type), target(&target_type)
        {
        }
        const std::type_info &source_type() const
        {
            return *source;
        }
        const std::type_info &target_type() const
        {
            return *target;
        }
        virtual const char *what() const throw()
        {
            return "bad lexical cast: "
                   "source type value could not be interpreted as target";
        }
        virtual ~bad_lexical_cast() throw()
        {
        }
    private:
        const std::type_info *source;
        const std::type_info *target;
    };

    namespace detail // selectors for choosing stream character type
    {
        template<typename Type>
        struct stream_char
        {
            typedef char type;
        };

        #ifndef DISABLE_WIDE_CHAR_SUPPORT
#if !defined(BOOST_NO_INTRINSIC_WCHAR_T)
        template<>
        struct stream_char<wchar_t>
        {
            typedef wchar_t type;
        };
#endif

        template<>
        struct stream_char<wchar_t *>
        {
            typedef wchar_t type;
        };

        template<>
        struct stream_char<const wchar_t *>
        {
            typedef wchar_t type;
        };

        template<>
        struct stream_char<std::wstring>
        {
            typedef wchar_t type;
        };
        #endif

        template<typename TargetChar, typename SourceChar>
        struct widest_char
        {
            typedef TargetChar type;
        };

        template<>
        struct widest_char<char, wchar_t>
        {
            typedef wchar_t type;
        };
    }
    
    namespace detail // stream wrapper for handling lexical conversions
    {
        template<typename Target, typename Source>
        class lexical_stream
        {
        private:
            typedef typename widest_char<
                typename stream_char<Target>::type,
                typename stream_char<Source>::type>::type char_type;

        public:
            lexical_stream()
            {
                stream.unsetf(std::ios::skipws);

                if(std::numeric_limits<Target>::is_specialized)
                    stream.precision(std::numeric_limits<Target>::digits10 + 1);
                else if(std::numeric_limits<Source>::is_specialized)
                    stream.precision(std::numeric_limits<Source>::digits10 + 1);
            }
            ~lexical_stream()
            {
                #if defined(BOOST_NO_STRINGSTREAM)
                stream.freeze(false);
                #endif
            }
            bool operator<<(const Source &input)
            {
                return !(stream << input).fail();
            }
            template<typename InputStreamable>
            bool operator>>(InputStreamable &output)
            {
                return !is_pointer<InputStreamable>::value &&
                       stream >> output &&
                       stream.get() ==
#if defined(__GNUC__) && (__GNUC__<3) && defined(BOOST_NO_STD_WSTRING)
// GCC 2.9x lacks std::char_traits<>::eof().
// We use BOOST_NO_STD_WSTRING to filter out STLport and libstdc++-v3
// configurations, which do provide std::char_traits<>::eof().
    
                           EOF;
#else
                           std::char_traits<char_type>::eof();
#endif
            }
            bool operator>>(std::string &output)
            {
                #if defined(BOOST_NO_STRINGSTREAM)
                stream << '\0';
                #endif
                output = stream.str();
                return true;
            }
            #ifndef DISABLE_WIDE_CHAR_SUPPORT
            bool operator>>(std::wstring &output)
            {
                output = stream.str();
                return true;
            }
            #endif
        private:
            #if defined(BOOST_NO_STRINGSTREAM)
            std::strstream stream;
            #elif defined(BOOST_NO_STD_LOCALE)
            std::stringstream stream;
            #else
            std::basic_stringstream<char_type> stream;
            #endif
        };
    }

    #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION

    // call-by-const reference version

    namespace detail
    {
        template<class T>
        struct array_to_pointer_decay
        {
            typedef T type;
        };

        template<class T, std::size_t N>
        struct array_to_pointer_decay<T[N]>
        {
            typedef const T * type;
        };
    }

    template<typename Target, typename Source>
    Target lexical_cast(const Source &arg)
    {
        typedef typename detail::array_to_pointer_decay<Source>::type NewSource;

        detail::lexical_stream<Target, NewSource> interpreter;
        Target result;

        if(!(interpreter << arg && interpreter >> result))
            throw_exception(bad_lexical_cast(typeid(NewSource), typeid(Target)));
        return result;
    }

    #else

    // call-by-value fallback version (deprecated)

    template<typename Target, typename Source>
    Target lexical_cast(Source arg)
    {
        detail::lexical_stream<Target, Source> interpreter;
        Target result;

        if(!(interpreter << arg && interpreter >> result))
            throw_exception(bad_lexical_cast(typeid(Source), typeid(Target)));
        return result;
    }

    #endif
}

// Copyright Kevlin Henney, 2000-2005. All rights reserved.
//
// 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)

#undef DISABLE_WIDE_CHAR_SUPPORT
#endif