`<iosfwd>`

Include the iostreams standard header <iosfwd> to declare forward references to several template classes used throughout iostreams. All such template classes are defined in other standard headers. You include this header explicitly only when you need one of the above declarations, but not its definition.

namespace std {
typedef T1 streamoff;
typedef T2 streamsize;
typedef fpos streampos;

       // TEMPLATE CLASSES
template<class Elem>
    class char_traits;
class char_traits<char>;
class char_traits<wchar_t>;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_ios;
template<class Elem, class Tr = char_traits<Elem> >
    class istreambuf_iterator;
template<class Elem, class Tr = char_traits<Elem> >
    class ostreambuf_iterator;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_streambuf;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_istream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_ostream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_iostream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_stringbuf;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_istringstream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_ostringstream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_stringstream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_filebuf;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_ifstream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_ofstream;
template<class Elem, class Tr = char_traits<Elem> >
    class basic_fstream;

        // char TYPE DEFINITIONS
typedef basic_ios<char, char_traits<char> > ios;
typedef basic_streambuf<char, char_traits<char> >
    streambuf;
typedef basic_istream<char, char_traits<char> >
    istream;
typedef basic_ostream<char, char_traits<char> >
    ostream;
typedef basic_iostream<char, char_traits<char> >
    iostream;
typedef basic_stringbuf<char, char_traits<char> >
    stringbuf;
typedef basic_istringstream<char, char_traits<char> >
    istringstream;
typedef basic_ostringstream<char, char_traits<char> >
    ostringstream;
typedef basic_stringstream<char, char_traits<char> >
    stringstream;
typedef basic_filebuf<char, char_traits<char> >
    filebuf;
typedef basic_ifstream<char, char_traits<char> >
    ifstream;
typedef basic_ofstream<char, char_traits<char> >
    ofstream;
typedef basic_fstream<char, char_traits<char> >
    fstream;

        // wchar_t TYPE DEFINITIONS
typedef basic_ios<wchar_t, char_traits<wchar_t> > wios;
typedef basic_streambuf<wchar_t, char_traits<wchar_t> >
    wstreambuf;
typedef basic_istream<wchar_t, char_traits<wchar_t> >
    wistream;
typedef basic_ostream<wchar_t, char_traits<wchar_t> >
    wostream;
typedef basic_iostream<wchar_t, char_traits<wchar_t> >
    wiostream;
typedef basic_stringbuf<wchar_t, char_traits<wchar_t> >
    wstringbuf;
typedef basic_istringstream<wchar_t,
    char_traits<wchar_t> > wistringstream;
typedef basic_ostringstream<wchar_t,
    char_traits<wchar_t> > wostringstream;
typedef basic_stringstream<wchar_t,
    char_traits<wchar_t> > wstringstream;
typedef basic_filebuf<wchar_t, char_traits<wchar_t> >
    wfilebuf;
typedef basic_ifstream<wchar_t, char_traits<wchar_t> >
    wifstream;
typedef basic_ofstream<wchar_t, char_traits<wchar_t> >
    wofstream;
typedef basic_fstream<wchar_t, char_traits<wchar_t> >
    wfstream;
    };

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