Namespaces
Variants

Standard library header <iosfwd>

From cppreference.net
C++
Standard library headers

此头文件包含对 输入/输出库 的前向声明。

前向声明

定义于头文件 <string>
std::char_traits 描述字符类型特性的类模板 (类模板)
std:: char_traits < char > （类模板特化）
std:: char_traits < wchar_t > （类模板特化）
std:: char_traits < char8_t > (C++20) (类模板特化)
std:: char_traits < char16_t > (C++11 起) (类模板特化)
std:: char_traits < char32_t > (C++11 起) (类模板特化)
定义于头文件 <memory>
默认分配器
(类模板)
定义于头文件 <ios>
管理任意流缓冲区
(类模板)
表示流或文件中的绝对位置
(类模板)
定义于头文件 <streambuf>
抽象原始设备
(类模板)
定义于头文件 <ostream>
封装给定的抽象设备（ std::basic_streambuf ）
并提供高层级输出接口
（类模板）
定义于头文件 <istream>
封装给定的抽象设备 ( std::basic_streambuf )
并提供高层级输入接口
(类模板)
封装给定的抽象设备（ std::basic_streambuf ）
并提供高层级输入/输出接口
（类模板）
定义于头文件 <fstream>
实现原始文件设备
(类模板)
实现高级文件流输入操作
(类模板)
实现高级文件流输出操作
(类模板)
实现高层级文件流输入/输出操作
(类模板)
定义于头文件 <sstream>
实现原始字符串设备
(类模板)
实现高级字符串流输入操作
(类模板)
实现高级字符串流输出操作
(类模板)
实现高级字符串流输入/输出操作
(类模板)
定义于头文件 <syncstream>
(C++20)
同步输出设备包装器
(类模板)
(C++20)
同步输出流包装器
(类模板)
定义于头文件 <spanstream>
(C++23)
实现原始固定字符缓冲区设备
(类模板)
(C++23)
实现固定字符缓冲区输入操作
(类模板)
(C++23)
实现固定字符缓冲区的输出操作
(类模板)
(C++23)
实现固定字符缓冲区的输入/输出操作
(类模板)
定义于头文件 <strstream>
(C++98 中已弃用) (C++26 中已移除)
实现原始字符数组设备
(类)
(C++98 中已弃用) (C++26 中已移除)
实现字符数组输入操作
(类)
(C++98 中已弃用) (C++26 中已移除)
实现字符数组输出操作
(类)
(C++98 中弃用) (C++26 中移除)
实现字符数组输入/输出操作
(类)

类型定义与特化

std::streampos std:: fpos < std:: char_traits < char > :: state_type >
std::wstreampos std:: fpos < std:: char_traits < wchar_t > :: state_type >
std::u8streampos std:: fpos < std:: char_traits < char8_t > :: state_type >
std::u16streampos std:: fpos < std:: char_traits < char16_t > :: state_type >
std::u32streampos std:: fpos < std:: char_traits < char32_t > :: state_type >
此外，对于在此头文件中声明的每个类模板 std::basic_ T ， std:: T 和 std::w T 分别被声明为 std::basic_ T <char> 和 std::basic_ T <wchar_t> 的同义词。

概要 

namespace std {
  template<class CharT> struct char_traits;
  template<> struct char_traits<char>;
  template<> struct char_traits<char8_t>;
  template<> struct char_traits<char16_t>;
  template<> struct char_traits<char32_t>;
  template<> struct char_traits<wchar_t>;
  template<class T> class allocator;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ios;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_streambuf;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_istream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ostream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_iostream;
  template<class CharT, class Traits = char_traits<CharT>,
           class Allocator = allocator<CharT>>
    class basic_stringbuf;
  template<class CharT, class Traits = char_traits<CharT>,
           class Allocator = allocator<CharT>>
    class basic_istringstream;
  template<class CharT, class Traits = char_traits<CharT>,
           class Allocator = allocator<CharT>>
    class basic_ostringstream;
  template<class CharT, class Traits = char_traits<CharT>,
           class Allocator = allocator<CharT>>
    class basic_stringstream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_filebuf;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ifstream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ofstream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_fstream;
  template<class CharT, class Traits = char_traits<CharT>,
           class Allocator = allocator<CharT>>
    class basic_syncbuf;
  template<class CharT, class Traits = char_traits<CharT>,
           class Allocator = allocator<CharT>>
    class basic_osyncstream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_spanbuf;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ispanstream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ospanstream;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_spanstream;
  template<class CharT, class Traits = char_traits<CharT>>
    class istreambuf_iterator;
  template<class CharT, class Traits = char_traits<CharT>>
    class ostreambuf_iterator;
  using ios  = basic_ios<char>;
  using wios = basic_ios<wchar_t>;
  using streambuf = basic_streambuf<char>;
  using istream   = basic_istream<char>;
  using ostream   = basic_ostream<char>;
  using iostream  = basic_iostream<char>;
  using stringbuf     = basic_stringbuf<char>;
  using istringstream = basic_istringstream<char>;
  using ostringstream = basic_ostringstream<char>;
  using stringstream  = basic_stringstream<char>;
  using filebuf  = basic_filebuf<char>;
  using ifstream = basic_ifstream<char>;
  using ofstream = basic_ofstream<char>;
  using fstream  = basic_fstream<char>;
  using syncbuf     = basic_syncbuf<char>;
  using osyncstream = basic_osyncstream<char>;
  using spanbuf     = basic_spanbuf<char>;
  using ispanstream = basic_ispanstream<char>;
  using ospanstream = basic_ospanstream<char>;
  using spanstream  = basic_spanstream<char>;
  using wstreambuf = basic_streambuf<wchar_t>;
  using wistream   = basic_istream<wchar_t>;
  using wostream   = basic_ostream<wchar_t>;
  using wiostream  = basic_iostream<wchar_t>;
  using wstringbuf     = basic_stringbuf<wchar_t>;
  using wistringstream = basic_istringstream<wchar_t>;
  using wostringstream = basic_ostringstream<wchar_t>;
  using wstringstream  = basic_stringstream<wchar_t>;
  using wfilebuf  = basic_filebuf<wchar_t>;
  using wifstream = basic_ifstream<wchar_t>;
  using wofstream = basic_ofstream<wchar_t>;
  using wfstream  = basic_fstream<wchar_t>;
  using wsyncbuf     = basic_syncbuf<wchar_t>;
  using wosyncstream = basic_osyncstream<wchar_t>;
  using wspanbuf     = basic_spanbuf<wchar_t>;
  using wispanstream = basic_ispanstream<wchar_t>;
  using wospanstream = basic_ospanstream<wchar_t>;
  using wspanstream  = basic_spanstream<wchar_t>;
  template<class State> class fpos;
  using streampos = fpos<char_traits<char>::state_type>;
  using wstreampos = fpos<char_traits<wchar_t>::state_type>;
  using u8streampos = fpos<char_traits<char8_t>::state_type>;
  using u16streampos = fpos<char_traits<char16_t>::state_type>;
  using u32streampos = fpos<char_traits<char32_t>::state_type>;
}
// deprecated
namespace std {
  class strstreambuf;
  class istrstream;
  class ostrstream;
  class strstream;
}