    // Copyright (C) 2005  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_SERIALIZe_
    #define DLIB_SERIALIZe_

    /*!
        There are two global functions in the dlib namespace that provide
        serialization and deserialization support.  Their signatures and specifications
        are as follows:

            void serialize (
                const serializable_type& item,
                std::ostream& out
            );
            /!*
                ensures
                    - writes the state of item to the output stream out
                    - if (serializable_type implements the enumerable interface) then
                        - item.at_start() == true
                throws
                    - serialization_error
                        This exception is thrown if there is some problem which prevents
                        us from successfully writing item to the output stream.
                    - any other exception
            *!/

            void deserialize (
                serializable_type& item,
                std::istream& in
            );
            /!*
                ensures
                    - #item == a deserialized copy of the serializable_type that was
                      in the input stream in.
                    - Reads all the bytes associated with the serialized serializable_type
                      contained inside the input stream and no more.  This means you
                      can serialize multiple objects to an output stream and then read
                      them all back in, one after another, using deserialize().
                    - if (serializable_type implements the enumerable interface) then
                        - item.at_start() == true
                throws
                    - serialization_error
                        This exception is thrown if there is some problem which prevents
                        us from successfully deserializing item from the input stream.
                        If this exception is thrown then item will have an initial value
                        for its type.
                    - any other exception
            *!/

        This file provides serialization support to the following object types:
            - The C++ base types (NOT including pointer types)
            - std::string
            - std::wstring
            - std::vector
            - std::map
            - std::set
            - std::pair
            - std::complex
            - dlib::uint64
            - dlib::int64
            - float_details
            - enumerable<T> where T is a serializable type
            - map_pair<D,R> where D and R are both serializable types.
            - C style arrays of serializable types
            - Google protocol buffer objects.

        This file provides deserialization support to the following object types:
            - The C++ base types (NOT including pointer types)
            - std::string
            - std::wstring
            - std::vector
            - std::map
            - std::set
            - std::pair
            - std::complex
            - dlib::uint64
            - dlib::int64
            - float_details
            - C style arrays of serializable types
            - Google protocol buffer objects.

        Support for deserialization of objects which implement the enumerable or
        map_pair interfaces is the responsibility of those objects.

        Note that you can deserialize an integer value to any integral type (except for a
        char type) if its value will fit into the target integer type.  I.e.  the types
        short, int, long, unsigned short, unsigned int, unsigned long, and dlib::uint64
        can all receive serialized data from each other so long as the actual serizlied
        value fits within the receiving integral type's range.

        Also note that for any container to be serializable the type of object it contains
        must be serializable.

        FILE STREAMS
            If you are serializing to and from file streams it is important to
            remember to set the file streams to binary mode using the std::ios::binary
            flag.

        INTEGRAL SERIALIZATION FORMAT
            All C++ integral types (except the char types) are serialized to the following
            format:
            The first byte is a control byte.  It tells you if the serialized number is
            positive or negative and also tells you how many of the following bytes are
            part of the number.  The absolute value of the number is stored in little
            endian byte order and follows the control byte.

            The control byte:
                The high order bit of the control byte is a flag that tells you if the
                encoded number is negative or not.  It is set to 1 when the number is
                negative and 0 otherwise.
                The 4 low order bits of the control byte represent an unsigned number
                and tells you how many of the following bytes are part of the encoded
                number.

        bool SERIALIZATION FORMAT
            A bool value is serialized as the single byte character '1' or '0' in ASCII.
            Where '1' indicates true and '0' indicates false.

        FLOATING POINT SERIALIZATION FORMAT
            To serialize a floating point value we convert it into a float_details object and
            then serialize the exponent and mantissa values using dlib's integral serialization
            format.  Therefore, the output is first the exponent and then the mantissa.  Note that
            the mantissa is a signed integer (i.e. there is not a separate sign bit).
    !*/

    #include "algs.h"
    #include "assert.h"
    #include <iomanip>
    #include <cstddef>
    #include <iostream>
    #include <string>
    #include <vector>
    #include <complex>
    #include <map>
    #include <set>
    #include <limits>
    #include "uintn.h"
    #include "interfaces/enumerable.h"
    #include "interfaces/map_pair.h"
    #include "enable_if.h"
    #include "unicode.h"
    #include "unicode.h"
    #include "byte_orderer.h"
    #include "float_details.h"

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        class serialization_error : public error
        {
        public:
            serialization_error(const std::string& e):error(e) {}
        };

    // ----------------------------------------------------------------------------------------

        namespace ser_helper
        {

            template <
                typename T
                >
            typename enable_if_c<std::numeric_limits<T>::is_signed,bool>::type pack_int (
                T item,
                std::ostream& out
            )
            /*!
                requires
                    - T is a signed integral type
                ensures
                    - if (no problems occur serializing item) then
                        - writes item to out
                        - returns false
                    - else
                        - returns true
            !*/
            {
                COMPILE_TIME_ASSERT(sizeof(T) <= 8);
                unsigned char buf[9];
                unsigned char size = sizeof(T);
                unsigned char neg;
                if (item < 0)
                {
                    neg = 0x80;
                    item *= -1;
                }
                else
                {
                    neg = 0;
                }

                for (unsigned char i = 1; i <= sizeof(T); ++i)
                {
                    buf[i] = static_cast<unsigned char>(item&0xFF);
                    item >>= 8;
                    if (item == 0) { size = i; break; }
                }

                std::streambuf* sbuf = out.rdbuf();
                buf[0] = size|neg;
                if (sbuf->sputn(reinterpret_cast<char*>(buf),size+1) != size+1)
                {
                    out.setstate(std::ios::eofbit | std::ios::badbit);
                    return true;
                }

                return false;
            }

        // ------------------------------------------------------------------------------------

            template <
                typename T
                >
            typename enable_if_c<std::numeric_limits<T>::is_signed,bool>::type unpack_int (
                T& item,
                std::istream& in
            )
            /*!
                requires
                    - T is a signed integral type
                ensures
                    - if (there are no problems deserializing item) then
                        - returns false
                        - #item == the value stored in in
                    - else
                        - returns true

            !*/
            {
                COMPILE_TIME_ASSERT(sizeof(T) <= 8);

                unsigned char buf[8];
                unsigned char size;
                bool is_negative;

                std::streambuf* sbuf = in.rdbuf();

                item = 0;
                int ch = sbuf->sbumpc();
                if (ch != EOF)
                {
                    size = static_cast<unsigned char>(ch);
                }
                else
                {
                    in.setstate(std::ios::badbit);
                    return true;
                }

                if (size&0x80)
                    is_negative = true;
                else
                    is_negative = false;
                size &= 0x0F;

                // check if the serialized object is too big
                if (size > sizeof(T))
                {
                    return true;
                }

                if (sbuf->sgetn(reinterpret_cast<char*>(&buf),size) != size)
                {
                    in.setstate(std::ios::badbit);
                    return true;
                }

                for (unsigned char i = size-1; true; --i)
                {
                    item <<= 8;
                    item |= buf[i];
                    if (i == 0)
                        break;
                }

                if (is_negative)
                    item *= -1;

                return false;
            }

        // ------------------------------------------------------------------------------------

            template <
                typename T
                >
            typename disable_if_c<std::numeric_limits<T>::is_signed,bool>::type pack_int (
                T item,
                std::ostream& out
            )
            /*!
                requires
                    - T is an unsigned integral type
                ensures
                    - if (no problems occur serializing item) then
                        - writes item to out
                        - returns false
                    - else
                        - returns true
            !*/
            {
                COMPILE_TIME_ASSERT(sizeof(T) <= 8);
                unsigned char buf[9];
                unsigned char size = sizeof(T);

                for (unsigned char i = 1; i <= sizeof(T); ++i)
                {
                    buf[i] = static_cast<unsigned char>(item&0xFF);
                    item >>= 8;
                    if (item == 0) { size = i; break; }
                }

                std::streambuf* sbuf = out.rdbuf();
                buf[0] = size;
                if (sbuf->sputn(reinterpret_cast<char*>(buf),size+1) != size+1)
                {
                    out.setstate(std::ios::eofbit | std::ios::badbit);
                    return true;
                }

                return false;
            }

        // ------------------------------------------------------------------------------------

            template <
                typename T
                >
            typename disable_if_c<std::numeric_limits<T>::is_signed,bool>::type unpack_int (
                T& item,
                std::istream& in
            )
            /*!
                requires
                    - T is an unsigned integral type
                ensures
                    - if (there are no problems deserializing item) then
                        - returns false
                        - #item == the value stored in in
                    - else
                        - returns true

            !*/
            {
                COMPILE_TIME_ASSERT(sizeof(T) <= 8);

                unsigned char buf[8];
                unsigned char size;

                item = 0;

                std::streambuf* sbuf = in.rdbuf();
                int ch = sbuf->sbumpc();
                if (ch != EOF)
                {
                    size = static_cast<unsigned char>(ch);
                }
                else
                {
                    in.setstate(std::ios::badbit);
                    return true;
                }

                // mask out the 3 reserved bits
                size &= 0x8F;

                // check if an error occurred
                if (size > sizeof(T))
                    return true;

                if (sbuf->sgetn(reinterpret_cast<char*>(&buf),size) != size)
                {
                    in.setstate(std::ios::badbit);
                    return true;
                }

                for (unsigned char i = size-1; true; --i)
                {
                    item <<= 8;
                    item |= buf[i];
                    if (i == 0)
                        break;
                }

                return false;
            }

        }

    // ----------------------------------------------------------------------------------------

        #define USE_DEFAULT_INT_SERIALIZATION_FOR(T)  \
            inline void serialize (const T& item, std::ostream& out) \
            { if (ser_helper::pack_int(item,out)) throw serialization_error("Error serializing object of type " + std::string(#T)); }   \
            inline void deserialize (T& item, std::istream& in) \
            { if (ser_helper::unpack_int(item,in)) throw serialization_error("Error deserializing object of type " + std::string(#T)); }

        template <typename T>
        inline bool pack_byte (
            const T& ch,
            std::ostream& out
        )
        {
            std::streambuf* sbuf = out.rdbuf();
            return (sbuf->sputc((char)ch) == EOF);
        }

        template <typename T>
        inline bool unpack_byte (
            T& ch,
            std::istream& in
        )
        {
            std::streambuf* sbuf = in.rdbuf();
            int temp = sbuf->sbumpc();
            if (temp != EOF)
            {
                ch = static_cast<T>(temp);
                return false;
            }
            else
            {
                return true;
            }
        }

        #define USE_DEFAULT_BYTE_SERIALIZATION_FOR(T)  \
            inline void serialize (const T& item,std::ostream& out) \
            { if (pack_byte(item,out)) throw serialization_error("Error serializing object of type " + std::string(#T)); } \
            inline void deserialize (T& item, std::istream& in) \
            { if (unpack_byte(item,in)) throw serialization_error("Error deserializing object of type " + std::string(#T)); }

    // ----------------------------------------------------------------------------------------

        USE_DEFAULT_INT_SERIALIZATION_FOR(short)
        USE_DEFAULT_INT_SERIALIZATION_FOR(int)
        USE_DEFAULT_INT_SERIALIZATION_FOR(long)
        USE_DEFAULT_INT_SERIALIZATION_FOR(unsigned short)
        USE_DEFAULT_INT_SERIALIZATION_FOR(unsigned int)
        USE_DEFAULT_INT_SERIALIZATION_FOR(unsigned long)
        USE_DEFAULT_INT_SERIALIZATION_FOR(uint64)
        USE_DEFAULT_INT_SERIALIZATION_FOR(int64)

        USE_DEFAULT_BYTE_SERIALIZATION_FOR(char)
        USE_DEFAULT_BYTE_SERIALIZATION_FOR(signed char)
        USE_DEFAULT_BYTE_SERIALIZATION_FOR(unsigned char)

        // Don't define serialization for wchar_t when using visual studio and
        // _NATIVE_WCHAR_T_DEFINED isn't defined since if it isn't they improperly set
        // wchar_t to be a typedef rather than its own type as required by the C++
        // standard.
    #if !defined(_MSC_VER) || _NATIVE_WCHAR_T_DEFINED
        USE_DEFAULT_INT_SERIALIZATION_FOR(wchar_t)
    #endif

    // ----------------------------------------------------------------------------------------

        inline void serialize(
            const float_details& item,
            std::ostream& out
        )
        {
            serialize(item.mantissa, out);
            serialize(item.exponent, out);
        }

        inline void deserialize(
            float_details& item,
            std::istream& in
        )
        {
            deserialize(item.mantissa, in);
            deserialize(item.exponent, in);
        }

    // ----------------------------------------------------------------------------------------

        template <typename T>
        inline void serialize_floating_point (
            const T& item,
            std::ostream& out
        )
        {
            try
            {
                float_details temp = item;
                serialize(temp, out);
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing a floating point number."); }
        }

        template <typename T>
        inline bool old_deserialize_floating_point (
            T& item,
            std::istream& in
        )
        {
            std::ios::fmtflags oldflags = in.flags();
            in.flags();
            std::streamsize ss = in.precision(35);
            if (in.peek() == 'i')
            {
                item = std::numeric_limits<T>::infinity();
                in.get();
                in.get();
                in.get();
            }
            else if (in.peek() == 'n')
            {
                item = -std::numeric_limits<T>::infinity();
                in.get();
                in.get();
                in.get();
                in.get();
            }
            else if (in.peek() == 'N')
            {
                item = std::numeric_limits<T>::quiet_NaN();
                in.get();
                in.get();
                in.get();
            }
            else
            {
                in >> item;
            }
            in.flags(oldflags);
            in.precision(ss);
            return (in.get() != ' ');
        }

        template <typename T>
        inline void deserialize_floating_point (
            T& item,
            std::istream& in
        )
        {
            // check if the serialized data uses the older ASCII based format.  We can check
            // this easily because the new format starts with the integer control byte which
            // always has 0 bits in the positions corresponding to the bitmask 0x70.  Moreover,
            // since the previous format used ASCII numbers we know that no valid bytes can
            // have bit values of one in the positions indicated 0x70.  So this test looks at
            // the first byte and checks if the serialized data uses the old format or the new
            // format.
            if ((in.rdbuf()->sgetc()&0x70) == 0)
            {
                try
                {
                    // Use the fast and compact binary serialization format.
                    float_details temp;
                    deserialize(temp, in);
                    item = temp;
                }
                catch (serialization_error& e)
                { throw serialization_error(e.info + "\n   while deserializing a floating point number."); }
            }
            else
            {
                if (old_deserialize_floating_point(item, in))
                    throw serialization_error("Error deserializing a floating point number.");
            }
        }

        inline void serialize ( const float& item, std::ostream& out)
        {
            serialize_floating_point(item,out);
        }

        inline void deserialize (float& item, std::istream& in)
        {
            deserialize_floating_point(item,in);
        }

        inline void serialize ( const double& item, std::ostream& out)
        {
            serialize_floating_point(item,out);
        }

        inline void deserialize (double& item, std::istream& in)
        {
            deserialize_floating_point(item,in);
        }

        inline void serialize ( const long double& item, std::ostream& out)
        {
            serialize_floating_point(item,out);
        }

        inline void deserialize ( long double& item, std::istream& in)
        {
            deserialize_floating_point(item,in);
        }

    // ----------------------------------------------------------------------------------------
    // prototypes

        template <typename domain, typename range, typename compare, typename alloc>
        void serialize (
            const std::map<domain,range, compare, alloc>& item,
            std::ostream& out
        );

        template <typename domain, typename range, typename compare, typename alloc>
        void deserialize (
            std::map<domain, range, compare, alloc>& item,
            std::istream& in
        );

        template <typename domain, typename compare, typename alloc>
        void serialize (
            const std::set<domain, compare, alloc>& item,
            std::ostream& out
        );

        template <typename domain, typename compare, typename alloc>
        void deserialize (
            std::set<domain, compare, alloc>& item,
            std::istream& in
        );

        template <typename T, typename alloc>
        void serialize (
            const std::vector<T,alloc>& item,
            std::ostream& out
        );

        template <typename T, typename alloc>
        void deserialize (
            std::vector<T,alloc>& item,
            std::istream& in
        );

        inline void serialize (
            const std::string& item,
            std::ostream& out
        );

        inline void deserialize (
            std::string& item,
            std::istream& in
        );

        template <
            typename T
            >
        inline void serialize (
            const enumerable<T>& item,
            std::ostream& out
        );

        template <
            typename domain,
            typename range
            >
        inline void serialize (
            const map_pair<domain,range>& item,
            std::ostream& out
        );

        template <
            typename T,
            size_t length
            >
        inline void serialize (
            const T (&array)[length],
            std::ostream& out
        );

        template <
            typename T,
            size_t length
            >
        inline void deserialize (
            T (&array)[length],
            std::istream& in
        );

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        inline void serialize (
            bool item,
            std::ostream& out
        )
        {
            if (item)
                out << '1';
            else
                out << '0';

            if (!out)
                throw serialization_error("Error serializing object of type bool");
        }

        inline void deserialize (
            bool& item,
            std::istream& in
        )
        {
            int ch = in.get();
            if (ch != EOF)
            {
                if (ch == '1')
                    item = true;
                else if (ch == '0')
                    item = false;
                else
                    throw serialization_error("Error deserializing object of type bool");
            }
            else
            {
                throw serialization_error("Error deserializing object of type bool");
            }
        }

    // ----------------------------------------------------------------------------------------

        template <typename first_type, typename second_type>
        void serialize (
            const std::pair<first_type, second_type>& item,
            std::ostream& out
        )
        {
            try
            {
                serialize(item.first,out);
                serialize(item.second,out);
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::pair"); }
        }

        template <typename first_type, typename second_type>
        void deserialize (
            std::pair<first_type, second_type>& item,
            std::istream& in
        )
        {
            try
            {
                deserialize(item.first,in);
                deserialize(item.second,in);
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::pair"); }
        }

    // ----------------------------------------------------------------------------------------

        template <typename domain, typename range, typename compare, typename alloc>
        void serialize (
            const std::map<domain,range, compare, alloc>& item,
            std::ostream& out
        )
        {
            try
            {
                const unsigned long size = static_cast<unsigned long>(item.size());

                serialize(size,out);
                typename std::map<domain,range,compare,alloc>::const_iterator i;
                for (i = item.begin(); i != item.end(); ++i)
                {
                    serialize(i->first,out);
                    serialize(i->second,out);
                }

            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::map"); }
        }

        template <typename domain, typename range, typename compare, typename alloc>
        void deserialize (
            std::map<domain, range, compare, alloc>& item,
            std::istream& in
        )
        {
            try
            {
                item.clear();

                unsigned long size;
                deserialize(size,in);
                domain d;
                range r;
                for (unsigned long i = 0; i < size; ++i)
                {
                    deserialize(d,in);
                    deserialize(r,in);
                    item[d] = r;
                }
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::map"); }
        }

    // ----------------------------------------------------------------------------------------

        template <typename domain, typename compare, typename alloc>
        void serialize (
            const std::set<domain, compare, alloc>& item,
            std::ostream& out
        )
        {
            try
            {
                const unsigned long size = static_cast<unsigned long>(item.size());

                serialize(size,out);
                typename std::set<domain,compare,alloc>::const_iterator i;
                for (i = item.begin(); i != item.end(); ++i)
                {
                    serialize(*i,out);
                }

            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::set"); }
        }

        template <typename domain, typename compare, typename alloc>
        void deserialize (
            std::set<domain, compare, alloc>& item,
            std::istream& in
        )
        {
            try
            {
                item.clear();

                unsigned long size;
                deserialize(size,in);
                domain d;
                for (unsigned long i = 0; i < size; ++i)
                {
                    deserialize(d,in);
                    item.insert(d);
                }
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::set"); }
        }

    // ----------------------------------------------------------------------------------------

        template <typename alloc>
        void serialize (
            const std::vector<bool,alloc>& item,
            std::ostream& out
        )
        {
            std::vector<unsigned char> temp(item.size());
            for (unsigned long i = 0; i < item.size(); ++i)
            {
                if (item[i])
                    temp[i] = '1';
                else
                    temp[i] = '0';
            }
            serialize(temp, out);
        }

        template <typename alloc>
        void deserialize (
            std::vector<bool,alloc>& item,
            std::istream& in
        )
        {
            std::vector<unsigned char> temp;
            deserialize(temp, in);
            item.resize(temp.size());
            for (unsigned long i = 0; i < temp.size(); ++i)
            {
                if (temp[i] == '1')
                    item[i] = true;
                else
                    item[i] = false;
            }
        }

    // ----------------------------------------------------------------------------------------

        template <typename T, typename alloc>
        void serialize (
            const std::vector<T,alloc>& item,
            std::ostream& out
        )
        {
            try
            {
                const unsigned long size = static_cast<unsigned long>(item.size());

                serialize(size,out);
                for (unsigned long i = 0; i < item.size(); ++i)
                    serialize(item[i],out);
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::vector"); }
        }

        template <typename T, typename alloc>
        void deserialize (
            std::vector<T, alloc>& item,
            std::istream& in
        )
        {
            try
            {
                unsigned long size;
                deserialize(size,in);
                item.resize(size);
                for (unsigned long i = 0; i < size; ++i)
                    deserialize(item[i],in);
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::vector"); }
        }

    // ----------------------------------------------------------------------------------------

        template <typename alloc>
        void serialize (
            const std::vector<char,alloc>& item,
            std::ostream& out
        )
        {
            try
            {
                const unsigned long size = static_cast<unsigned long>(item.size());
                serialize(size,out);
                if (item.size() != 0)
                    out.write(&item[0], item.size());
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::vector"); }
        }

        template <typename alloc>
        void deserialize (
            std::vector<char, alloc>& item,
            std::istream& in
        )
        {
            try
            {
                unsigned long size;
                deserialize(size,in);
                item.resize(size);
                if (item.size() != 0)
                    in.read(&item[0], item.size());
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::vector"); }
        }

    // ----------------------------------------------------------------------------------------

        template <typename alloc>
        void serialize (
            const std::vector<unsigned char,alloc>& item,
            std::ostream& out
        )
        {
            try
            {
                const unsigned long size = static_cast<unsigned long>(item.size());
                serialize(size,out);
                if (item.size() != 0)
                    out.write((char*)&item[0], item.size());
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::vector"); }
        }

        template <typename alloc>
        void deserialize (
            std::vector<unsigned char, alloc>& item,
            std::istream& in
        )
        {
            try
            {
                unsigned long size;
                deserialize(size,in);
                item.resize(size);
                if (item.size() != 0)
                    in.read((char*)&item[0], item.size());
            }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::vector"); }
        }

    // ----------------------------------------------------------------------------------------

        inline void serialize (
            const std::string& item,
            std::ostream& out
        )
        {
            const unsigned long size = static_cast<unsigned long>(item.size());
            try{ serialize(size,out); }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::string"); }

            out.write(item.c_str(),size);
            if (!out) throw serialization_error("Error serializing object of type std::string");
        }

        inline void deserialize (
            std::string& item,
            std::istream& in
        )
        {
            unsigned long size;
            try { deserialize(size,in); }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::string"); }

            item.resize(size);
            if (size != 0)
            {
                in.read(&item[0],size);
                if (!in) throw serialization_error("Error deserializing object of type std::string");
            }
        }

    // ----------------------------------------------------------------------------------------

        inline void serialize (
            const std::wstring& item,
            std::ostream& out
        )
        {
            const unsigned long size = static_cast<unsigned long>(item.size());
            try{ serialize(size,out); }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type std::wstring"); }

            for (unsigned long i = 0; i < item.size(); ++i)
                serialize(item[i], out);
            if (!out) throw serialization_error("Error serializing object of type std::wstring");
        }

        inline void deserialize (
            std::wstring& item,
            std::istream& in
        )
        {
            unsigned long size;
            try { deserialize(size,in); }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type std::wstring"); }

            item.resize(size);
            for (unsigned long i = 0; i < item.size(); ++i)
                deserialize(item[i],in);

            if (!in) throw serialization_error("Error deserializing object of type std::wstring");
        }

    // ----------------------------------------------------------------------------------------

        inline void serialize (
            const ustring& item,
            std::ostream& out
        )
        {
            const unsigned long size = static_cast<unsigned long>(item.size());
            try{ serialize(size,out); }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while serializing object of type ustring"); }

            for (unsigned long i = 0; i < item.size(); ++i)
                serialize(item[i], out);
            if (!out) throw serialization_error("Error serializing object of type ustring");
        }

        inline void deserialize (
            ustring& item,
            std::istream& in
        )
        {
            unsigned long size;
            try { deserialize(size,in); }
            catch (serialization_error& e)
            { throw serialization_error(e.info + "\n   while deserializing object of type ustring"); }

            item.resize(size);
            for (unsigned long i = 0; i < item.size(); ++i)
                deserialize(item[i],in);

            if (!in) throw serialization_error("Error deserializing object of type ustring");
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T
            >
        inline void serialize (
            const enumerable<T>& item,
            std::ostream& out
        )
        {
            try
            {
                item.reset();
                serialize(item.size(),out);
                while (item.move_next())
                    serialize(item.element(),out);
                item.reset();
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while serializing object of type enumerable");
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename domain,
            typename range
            >
        inline void serialize (
            const map_pair<domain,range>& item,
            std::ostream& out
        )
        {
            try
            {
                serialize(item.key(),out);
                serialize(item.value(),out);
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while serializing object of type map_pair");
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            size_t length
            >
        inline void serialize (
            const T (&array)[length],
            std::ostream& out
        )
        {
            try
            {
                serialize(length,out);
                for (size_t i = 0; i < length; ++i)
                    serialize(array[i],out);
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while serializing a C style array");
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            size_t length
            >
        inline void deserialize (
            T (&array)[length],
            std::istream& in
        )
        {
            size_t size;
            try
            {
                deserialize(size,in);
                if (size == length)
                {
                    for (size_t i = 0; i < length; ++i)
                        deserialize(array[i],in);
                }
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while deserializing a C style array");
            }

            if (size != length)
                throw serialization_error("Error deserializing a C style array, lengths do not match");
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T
            >
        inline void serialize (
            const std::complex<T>& item,
            std::ostream& out
        )
        {
            try
            {
                serialize(item.real(),out);
                serialize(item.imag(),out);
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while serializing an object of type std::complex");
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T
            >
        inline void deserialize (
            std::complex<T>& item,
            std::istream& in
        )
        {
            try
            {
                T real, imag;
                deserialize(real,in);
                deserialize(imag,in);
                item = std::complex<T>(real,imag);
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while deserializing an object of type std::complex");
            }
        }

    // ----------------------------------------------------------------------------------------
    }

    // forward declare the MessageLite object so we can reference it below.
    namespace google
    {
        namespace protobuf
        {
            class MessageLite;
        }
    }

    namespace dlib
    {

        /*!A is_protocol_buffer
            This is a template that tells you if a type is a Google protocol buffer object.
        !*/

        template <typename T, typename U = void >
        struct is_protocol_buffer
        {
            static const bool value = false;
        };

        template <typename T>
        struct is_protocol_buffer <T,typename enable_if<is_convertible<T*,::google::protobuf::MessageLite*> >::type  >
        {
            static const bool value = true;
        };

        template <typename T>
        typename enable_if<is_protocol_buffer<T> >::type serialize(const T& item, std::ostream& out)
        {
            // Note that Google protocol buffer messages are not self delimiting
            // (see https://developers.google.com/protocol-buffers/docs/techniques)
            // This means they don't record their length or where they end, so we have
            // to record this information ourselves.  So we save the size as a little endian 32bit
            // integer prefixed onto the front of the message.

            byte_orderer bo;

            // serialize into temp string
            std::string temp;
            if (!item.SerializeToString(&temp))
                throw dlib::serialization_error("Error while serializing a Google Protocol Buffer object.");
            if (temp.size() > std::numeric_limits<uint32>::max())
                throw dlib::serialization_error("Error while serializing a Google Protocol Buffer object, message too large.");

            // write temp to the output stream
            uint32 size = temp.size();
            bo.host_to_little(size);
            out.write((char*)&size, sizeof(size));
            out.write(temp.c_str(), temp.size());
        }

        template <typename T>
        typename enable_if<is_protocol_buffer<T> >::type deserialize(T& item, std::istream& in)
        {
            // Note that Google protocol buffer messages are not self delimiting
            // (see https://developers.google.com/protocol-buffers/docs/techniques)
            // This means they don't record their length or where they end, so we have
            // to record this information ourselves.  So we save the size as a little endian 32bit
            // integer prefixed onto the front of the message.

            byte_orderer bo;

            uint32 size = 0;
            // read the size
            in.read((char*)&size, sizeof(size));
            bo.little_to_host(size);
            if (!in || size == 0)
                throw dlib::serialization_error("Error while deserializing a Google Protocol Buffer object.");

            // read the bytes into temp
            std::string temp;
            temp.resize(size);
            in.read(&temp[0], size);

            // parse temp into item
            if (!in || !item.ParseFromString(temp))
            {
                throw dlib::serialization_error("Error while deserializing a Google Protocol Buffer object.");
            }
        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_SERIALIZe_