标准库头文件 <iosfwd>

 

C++

编译器支持

独立和托管

语言

标准库

标准库头文件

命名需求

特性测试宏 (C++20)

语言支持库

概念库 (C++20)

元编程库 (C++11)

诊断库

通用实用程序库

字符串库

容器库

迭代器库

范围库 (C++20)

算法库

数值库

本地化库

输入/输出库

文件系统库 (C++17)

正则表达式库 (C++11)

并发支持库 (C++11)

执行支持库 (C++26)

技术规范

符号索引

外部库

 

标准库头文件

语言支持
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <stdfloat> (C++23) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11) <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
概念
<concepts> (C++20)
诊断
<stdexcept> <stacktrace> (C++23)	<cassert>	<cerrno>	<system_error> (C++11)
内存管理
<memory>	<memory_resource> (C++17)	<scoped_allocator> (C++11)
元编程
<type_traits> (C++11)	<ratio> (C++11)
通用实用程序
<utility> <tuple> (C++11) <optional> (C++17) <variant> (C++17)	<any> (C++17) <debugging> (C++26) <expected> (C++23) <bitset>	<functional> <typeindex> (C++11) <execution> (C++17)	<charconv> (C++17) <format> (C++20) <bit> (C++20)
字符串
<string_view> (C++17) <string>	<cctype> <cwctype>	<cstring> <cwchar>	<cuchar> (C++11)
容器
<array> (C++11) <deque> <forward_list> (C++11) <list>	<vector> <map> <set> <unordered_map> (C++11)	<unordered_set> (C++11) <queue> <stack> <flat_map> (C++23)	<flat_set> (C++23) <span> (C++20) <mdspan> (C++23) <inplace_vector> (C++26)
迭代器
<iterator>
范围
<ranges> (C++20)	<generator> (C++23)
算法
<algorithm>	<numeric>
数值
<cfenv> (C++11) <complex>	<random> (C++11) <valarray>	<cmath> <linalg> (C++26)	<numbers> (C++20)
时间
<chrono> (C++11)	<ctime>
本地化
<locale>	<clocale>	<codecvt> (C++11/17/26*)	<text_encoding> (C++26)
输入/输出
<iosfwd> <iostream> <ios> <streambuf>	<istream> <ostream> <iomanip> <print> (C++23)	<sstream> <spanstream> (C++23) <fstream> <syncstream> (C++20)	<filesystem> (C++17) <cstdio> <cinttypes> (C++11) <strstream> (C++98/26*)
正则表达式
<regex> (C++11)
并发支持
<stop_token> (C++20) <thread> (C++11) <atomic> (C++11) <rcu> (C++26)	<stdatomic.h> (C++23) <mutex> (C++11) <shared_mutex> (C++14)	<condition_variable> (C++11)   <semaphore> (C++20) <latch> (C++20)	<barrier> (C++20) <future> (C++11) <hazard_pointer> (C++26)
C 兼容性
<cstdbool> (C++11/17/20*)   <ccomplex> (C++11/17/20*)	<ctgmath> (C++11/17/20*)	<cstdalign> (C++11/17/20*)	<ciso646> (直到 C++20)

 

此头文件包含 输入/输出 库的前向声明。

前向声明
定义在头文件 <string> 中
std::char_traits	描述字符类型属性的类模板 (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)	(类模板特化)
std::char_traits<char32_t> (C++11)	(类模板特化)
在头文件 <memory> 中定义
分配器	默认分配器 (类模板)
在头文件 <ios> 中定义
basic_ios	管理任意流缓冲区 (类模板)
fpos	表示流或文件中的绝对位置 (类模板)
在头文件 <streambuf> 中定义
basic_streambuf	抽象化原始设备 (类模板)
在头文件 <ostream> 中定义
basic_ostream	封装给定的抽象设备 (std::basic_streambuf) 并提供高级输出接口 (类模板)
在头文件 <istream> 中定义
basic_istream	封装给定的抽象设备 (std::basic_streambuf) 并提供高级输入接口 (类模板)
basic_iostream	封装给定的抽象设备 (std::basic_streambuf) 并提供高级输入/输出接口 (类模板)
在头文件 <fstream> 中定义
basic_filebuf	实现原始文件设备 (类模板)
basic_ifstream	实现高级文件流输入操作 (类模板)
basic_ofstream	实现高级文件流输出操作 (类模板)
basic_fstream	实现高级文件流输入/输出操作 (类模板)
在头文件 <sstream> 中定义
basic_stringbuf	实现原始字符串设备 (类模板)
basic_istringstream	实现高级字符串流输入操作 (类模板)
basic_ostringstream	实现高级字符串流输出操作 (类模板)
basic_stringstream	实现高级字符串流输入/输出操作 (类模板)
在头文件 <syncstream> 中定义
basic_syncbuf (C++20)	同步输出设备包装器 (类模板)
basic_osyncstream (C++20)	同步输出流包装器 (类模板)
在头文件 <spanstream> 中定义
basic_spanbuf (C++23)	实现原始固定字符缓冲区设备 (类模板)
basic_ispanstream (C++23)	实现固定字符缓冲区输入操作 (类模板)
basic_ospanstream (C++23)	实现固定字符缓冲区输出操作 (类模板)
basic_spanstream (C++23)	实现固定字符缓冲区输入/输出操作 (类模板)
在头文件 <strstream> 中定义
strstreambuf (C++98 中已弃用)(C++26 中已移除)	实现原始字符数组设备 (类)
istrstream (C++98 中已弃用)(C++26 中已移除)	实现字符数组输入操作 (类)
ostrstream (C++98 中已弃用)(C++26 中已移除)	实现字符数组输出操作 (类)
strstream (C++98 中已弃用)(C++26 中已移除)	实现字符数组输入/输出操作 (类)
类型定义和特化
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，对于在本头文件中声明的每个类模板 std::basic_T，std::T 和 std::wT 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;
}