<iosfwd>
Declares forward references to several class templates used throughout iostreams. All such class templates are defined in other standard headers. You include this header explicitly only when you need one of its declarations, but not its definition.
#include <iosfwd>
typedef T1 streamoff;
typedef T2 streamsize;
typedef fpos streampos;
// 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;
template <class _Statetype>
class fpos;
template <class Elem>;
class char_traits;
class char_traits<char>;
class char_traits<wchar_t>;
template <class T>
class allocator;
class ios_base;
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;
Header Files Reference
Thread Safety in the C++ Standard Library
iostream Programming
iostreams Conventions