标准库标头 <iosfwd>

 

C++

编译器支持

自立实现与有宿主实现

语言

标准库

标准库标头

具名要求

功能特性测试宏(C++20)

语言支持库

概念库(C++20)

诊断库

内存管理库

元编程库(C++11)

通用工具库

容器库

迭代器库

范围库(C++20)

算法库

字符串库

文本处理库

数值库

日期和时间库

输入/输出库

文件系统库(C++17)

并发支持库(C++11)

执行控制库(C++26)

技术规范

符号索引

外部库

 

标准库头

语言支持 <cfloat> <climits> <compare>(C++20) <contracts>(C++26) <coroutine>(C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint>(C++11) <cstdlib> <exception> <initializer_list>(C++11)    <limits> <new> <source_location>(C++20) <stdfloat>(C++23) <typeinfo> <version>(C++20) 概念 <concepts>(C++20) 诊断 <cassert> <cerrno> <debugging>(C++26) <stacktrace>(C++23) <stdexcept> <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)

通用工具 <any>(C++17) <bitset> <bit>(C++20) <charconv>(C++17) <expected>(C++23) <format>(C++20) <functional> <optional>(C++17) <stdbit.h>(C++26) <tuple>(C++11) <typeindex>(C++11) <utility> <variant>(C++17) 容器 <array>(C++11) <deque> <flat_map>(C++23) <flat_set>(C++23) <forward_list>(C++11) <hive>(C++26) <inplace_vector>(C++26)    <list> <map> <mdspan>(C++23) <queue> <set> <span>(C++20) <stack> <unordered_map>(C++11) <unordered_set>(C++11) <vector> 迭代器 <iterator> 范围 <generator>(C++23) <ranges>(C++20)

算法 <algorithm> <numeric> 字符串 <cctype> <cstring> <cuchar>(C++11) <cwchar> <cwctype> <string_view>(C++17) <string> 文本处理 <clocale> <codecvt>(C++11/17/26*) <locale> <regex>(C++11) <text_encoding>(C++26)    cpp/header#数值库数值 <cfenv>(C++11) <cmath> <complex> <linalg>(C++26) <numbers>(C++20) <random>(C++11) <simd>(C++26) <stdckdint.h>(C++26) <valarray> 时间 <chrono>(C++11) <ctime> C 兼容性 <ccomplex>(C++11/17/20*) <ciso646>(C++20 前) <cstdalign>(C++11/17/20*) <cstdbool>(C++11/17/20*) <ctgmath>(C++11/17/20*)

输入/输出 <cinttypes>(C++11) <cstdio> <filesystem>(C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print>(C++23) <spanstream>(C++23) <sstream> <streambuf> <strstream>(C++98/26*) <syncstream>(C++20) 并发支持 <atomic>(C++11) <barrier>(C++20) <condition_variable>(C++11) <future>(C++11) <hazard_pointer>(C++26) <latch>(C++20) <mutex>(C++11) <rcu>(C++26) <semaphore>(C++20) <shared_mutex>(C++14) <stdatomic.h>(C++23) <stop_token>(C++20) <thread>(C++11) 执行支持 <execution>(C++17)

 

此头文件含有输入/输出库的前置声明。

前置声明
在标头 <string> 定义
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)
在标头 <memory> 定义
allocator	默认的分配器 (类模板)
在标头 <ios> 定义
basic_ios	管理任意流缓冲 (类模板)
fpos	表示流或文件中的绝对位置 (类模板)
在标头 <streambuf> 定义
basic_streambuf	抽象原生设备 (类模板)
在标头 <ostream> 定义
basic_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)
在标头 <istream> 定义
basic_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)
basic_iostream	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)
在标头 <fstream> 定义
basic_filebuf	实现原生文件设备 (类模板)
basic_ifstream	实现高层文件流输入操作 (类模板)
basic_ofstream	实现高层文件流输出操作 (类模板)
basic_fstream	实现高层文件流输入/输出操作 (类模板)
在标头 <sstream> 定义
basic_stringbuf	实现原生字符串设备 (类模板)
basic_istringstream	实现高层字符串流输入操作 (类模板)
basic_ostringstream	实现高层字符串流输出操作 (类模板)
basic_stringstream	实现高层字符串流输入/输出操作 (类模板)
在标头 <syncstream> 定义
basic_syncbuf (C++20)	同步输出设备的包装器 (类模板)
basic_osyncstream (C++20)	同步输出流的包装器 (类模板)
在标头 <spanstream> 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)
在标头 <strstream> 定义
strstreambuf (C++98 弃用)(C++26 移除)	实现原生字符数组设备 (类)
istrstream (C++98 弃用)(C++26 移除)	实现字符数组输入操作 (类)
ostrstream (C++98 弃用)(C++26 移除)	实现字符数组输出操作 (类)
strstream (C++98 弃用)(C++26 移除)	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 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>;}   // 弃用namespace std {class strstreambuf;class istrstream;class ostrstream;class strstream;}