标准库头文件 <iosfwd>

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C++
 
标准库头文件
语言支持
概念
<concepts>
诊断
通用工具
字符串
本地化
容器
迭代器
<iterator>
范围
<ranges>
算法
数值
输入/输出
正则表达式
<regex>
文件系统
<filesystem>
线程支持
C 兼容
 

此头文件含有输入/输出库的前置声明。

前置声明

定义于头文件 <string>
std::char_traits 描述字符类型的性质的类模板 (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) (类模板特化)
std::char_traits<char32_t> (C++11) (类模板特化)
定义于头文件 <memory>
默认的分配器
(类模板)
定义于头文件 <ios>
管理任意流缓冲
(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>
抽象原生设备
(类模板)
定义于头文件 <ostream>
包装给定的抽象设备（std::basic_streambuf）
并提供高层输出接口
(类模板)
定义于头文件 <istream>
包装给定的抽象设备（std::basic_streambuf）
并提供高层输入接口
(类模板)
包装给定的抽象设备（std::basic_streambuf）
并提供高层输入/输出接口
(类模板)
定义于头文件 <fstream>
抽象原生文件设备
(类模板)
实现高层文件流输入操作
(类模板)
实现高层文件流输出操作
(类模板)
实现高层文件流输入/输出操作
(类模板)
定义于头文件 <sstream>
实现原生字符串设备
(类模板)
实现高层字符串流输入操作
(类模板)
实现高层字符串流输出操作
(类模板)
实现高层字符串流输入/输出操作
(类模板)
定义于头文件 <syncstream>
(C++20)
 同步输出设备的包装
(类模板)
(C++20)
 同步输出流的包装
(类模板)
定义于头文件 <strstream>
(C++98 中弃用)
 实现原生字符数组设备
(类)
(C++98 中弃用)
 实现字符数组输入操作
(类)
(C++98 中弃用)
 实现字符数组输出操作
(类)
(C++98 中弃用)
 实现字符数组输入/输出操作
(类)

typedef 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>
另外，对于每个声明于此头文件的类模板 std::basic_T，分别声明了 std::T 和 std::wT 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 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 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>;
 
  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>;
}
 
// 弃用
namespace std {
  class strstreambuf;
  class istrstream;
  class ostrstream;
  class strstream;
}
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