<iosfwd>
宣告整個iostream中使用的數個類別範本的轉送參考。 所有這類類別範本都定義在其他標準標頭中。 只有當您需要此標頭的其中一個宣告但不需要其定義時，才需要明確包含此標頭。
語法
#include <iosfwd>
Typedefs
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;
轉送宣告和類別範本
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;