摘要：
Iomanistream:：get；C++标准库；istream和istream：：getline；函数：从文本中提取指定数量的字符串，并在字符串数组的末尾添加一个空字符。区别：get（）不会从流中提取终止字符，并且终止字符仍在输入流中。getline（）从流中提取终止字符，但终止字符被丢弃。C++语言头文件：#includedomanip描述：它是一个I/O流控制头文件，就像C，1setiosflags中的格式化输出一样，用于设置格式标志。
C++ 标准库之iomanip
istream & istream::get(char *, int, char = ‘ ’);
istream & istream::getline(char *, int, char = ‘ ’);
作用: 从文本中提取指定个数的字符串, 并在串数组末尾添加一个空字符.
区别: get() 不从流中提取终止字符, 终止字符仍在输入流中. getline() 从流中提取终止字符, 但终止字符被丢弃.
C++ 语言下
头文件：#include iomanip
说明：是I/O流控制头文件,就像C里面的格式化输出一样
1 setiosflags - 它用于设置格式标志。
2 resetiosflags - 用于重置格式标志。
3 setbase - 它用于设置basefield标志。
4 setfill - 它用于设置填充字符
5 setprecision - 它用于设置小数精度。
6 setw - 它用于设置字段宽度。
7 get_money - 它用于获得货币值。
8 put_money - 它用来设置计算货币的值。
9 get_time - 它用于获取日期和时间。
10 put_time - 它用于放置（或设置）日期和时间。
dec 设置整数为十进制
hex 设置整数为十六进制
oct 设置整数为八进制
setbase(n) 设置整数为n进制(n=8,10,16)
setfill(n)
设置字符填充，c可以是字符常或字符变量
setprecision(n) 设置浮点数的有效数字为n位
setw(n) 设置字段宽度为n位
setiosflags(ios::fixed) 设置浮点数以固定的小数位数显示
setiosflags(ios::scientific) 设置浮点数以科学计数法表示
setiosflags(ios::left) 输出左对齐
setiosflags(ios::right) 输出右对齐
setiosflags(ios::skipws) 忽略前导空格
setiosflags(ios::uppercase) 在以科学计数法输出E与十六进制输出X以大写输出，否则小写。
setiosflags(ios::showpos) 输出正数时显示"+"号
setiosflags(ios::showpoint) 强制显示小数点
resetiosflags()
终止已经设置的输出格式状态，在括号中应指定内容
在此需要说一下，有效位数默认是6位，即setprecision(6)，即小数点前面和小数点后面加起来的位数为6个有效数字（注意会四舍五入）。
另外，科学计数法输出E与十六进制输出默认是以小写的，要换成大写需添加uppercase
而setw(n)设置宽度，若是实际宽度大于被设置的，则setw函数此时失效。
下面是各种函数代码：
#include <iostream>
#include <iomanip>
#include <fstream>
int main()
{
// 前缀0表示八进制 前缀0x表示十六进制 不带前缀表示十进制
int a = 123;
double pi = 22.0/7.0;
// setbase(n) 设置整数为n进制(n=8,10,16)
// oct 八进制 dec 十进制 hex 十六进制
// setiosflags(ios::showbase) 显示进制的前缀
// 数值默认十进制显示输出
std::cout << a << std::endl;
std::cout << "oct: " << std::showbase << std::setbase(8) << a << " " << std::oct << a << std::endl;
std::cout << "dec: " << std::showbase << std::setbase(10) << a << " " << std::dec << a << std::endl;
std::cout << "hex: " << std::showbase << std::setbase(16) << a << " " << std::hex << a << std::endl;
// setprecision(n) 设置浮点数的有效数字为n位
// 有效位数默认是6位，即setprecision(6)，即小数点前面和小数点后面加起来的位数为6个有效数字（注意会四舍五入）
std::cout << pi << std::endl;
std::cout << std::setprecision(12) << pi << std::endl;
// setfill(n) 设置字符填充，c可以是字符常或字符变量
// setw(n) 设置字段宽度为n位, 若是实际宽度大于被设置的，则setw函数此时失效, 只针对其后的第一个输出项有效
// setiosflags(ios::left) 输出左对齐
// setiosflags(ios::right) 输出右对齐 默认右对齐
std::cout << std::setfill('*') << std::setw(20) << std::setprecision(12) << pi << std::endl;
std::cout << std::setfill('*') << std::setw(20) << std::setprecision(12) << std::right << pi << std::endl;
std::cout << std::setfill('*') << std::setw(20) << std::setprecision(12) << std::left << pi << std::endl;
// setiosflags(ios::fixed) 设置浮点数以固定的小数位数显示
std::cout << std::fixed << std::setprecision(12) << pi << std::endl;
// setiosflags(ios::scientific) 设置浮点数以科学计数法表示 科学计数法输出E与十六进制输出默认是以小写的，要换成大写需添加uppercase
std::cout << std::scientific << std::setprecision(12) << pi << std::endl;
std::cout << std::scientific << std::uppercase << std::setprecision(12) << pi << std::endl;
// resetiosflags() 终止已经设置的输出格式状态，在括号中应指定内容
std::cout << std::setiosflags(std::ios::scientific) << std::setprecision(12) << pi << " " << std::resetiosflags(std::ios::scientific) << pi << std::endl;
system("pause");
return 0;
}
Dev-C++ 中iomanip头文件内容：
// Standard stream manipulators -*- C++ -*-
// Copyright (C) 1997-2014 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file include/iomanip
* This is a Standard C++ Library header.
*/
//
// ISO C++ 14882: 27.6.3 Standard manipulators
//
#ifndef _GLIBCXX_IOMANIP
#define _GLIBCXX_IOMANIP 1
#pragma GCC system_header
#include <bits/c++config.h>
#include <iosfwd>
#include <bits/ios_base.h>
#if __cplusplus >= 201103L
#include <locale>
#if __cplusplus > 201103L
#include <sstream> // used in quoted.
#endif
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
// [27.6.3] standard manipulators
// Also see DR 183.
struct _Resetiosflags { ios_base::fmtflags _M_mask; };
/**
* @brief Manipulator for @c setf.
* @param __mask A format flags mask.
*
* Sent to a stream object, this manipulator resets the specified flags,
* via @e stream.setf(0,__mask).
*/
inline _Resetiosflags
resetiosflags(ios_base::fmtflags __mask)
{ return { __mask }; }
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Resetiosflags __f)
{
__is.setf(ios_base::fmtflags(0), __f._M_mask);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Resetiosflags __f)
{
__os.setf(ios_base::fmtflags(0), __f._M_mask);
return __os;
}
struct _Setiosflags { ios_base::fmtflags _M_mask; };
/**
* @brief Manipulator for @c setf.
* @param __mask A format flags mask.
*
* Sent to a stream object, this manipulator sets the format flags
* to @a __mask.
*/
inline _Setiosflags
setiosflags(ios_base::fmtflags __mask)
{ return { __mask }; }
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setiosflags __f)
{
__is.setf(__f._M_mask);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setiosflags __f)
{
__os.setf(__f._M_mask);
return __os;
}
struct _Setbase { int _M_base; };
/**
* @brief Manipulator for @c setf.
* @param __base A numeric base.
*
* Sent to a stream object, this manipulator changes the
* @c ios_base::basefield flags to @c oct, @c dec, or @c hex when @a base
* is 8, 10, or 16, accordingly, and to 0 if @a __base is any other value.
*/
inline _Setbase
setbase(int __base)
{ return { __base }; }
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setbase __f)
{
__is.setf(__f._M_base == 8 ? ios_base::oct :
__f._M_base == 10 ? ios_base::dec :
__f._M_base == 16 ? ios_base::hex :
ios_base::fmtflags(0), ios_base::basefield);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setbase __f)
{
__os.setf(__f._M_base == 8 ? ios_base::oct :
__f._M_base == 10 ? ios_base::dec :
__f._M_base == 16 ? ios_base::hex :
ios_base::fmtflags(0), ios_base::basefield);
return __os;
}
template<typename _CharT>
struct _Setfill { _CharT _M_c; };
/**
* @brief Manipulator for @c fill.
* @param __c The new fill character.
*
* Sent to a stream object, this manipulator calls @c fill(__c) for that
* object.
*/
template<typename _CharT>
inline _Setfill<_CharT>
setfill(_CharT __c)
{ return { __c }; }
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setfill<_CharT> __f)
{
__is.fill(__f._M_c);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setfill<_CharT> __f)
{
__os.fill(__f._M_c);
return __os;
}
struct _Setprecision { int _M_n; };
/**
* @brief Manipulator for @c precision.
* @param __n The new precision.
*
* Sent to a stream object, this manipulator calls @c precision(__n) for
* that object.
*/
inline _Setprecision
setprecision(int __n)
{ return { __n }; }
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setprecision __f)
{
__is.precision(__f._M_n);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setprecision __f)
{
__os.precision(__f._M_n);
return __os;
}
struct _Setw { int _M_n; };
/**
* @brief Manipulator for @c width.
* @param __n The new width.
*
* Sent to a stream object, this manipulator calls @c width(__n) for
* that object.
*/
inline _Setw
setw(int __n)
{ return { __n }; }
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setw __f)
{
__is.width(__f._M_n);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setw __f)
{
__os.width(__f._M_n);
return __os;
}
#if __cplusplus >= 201103L
template<typename _MoneyT>
struct _Get_money { _MoneyT& _M_mon; bool _M_intl; };
/**
* @brief Extended manipulator for extracting money.
* @param __mon Either long double or a specialization of @c basic_string.
* @param __intl A bool indicating whether international format
* is to be used.
*
* Sent to a stream object, this manipulator extracts @a __mon.
*/
template<typename _MoneyT>
inline _Get_money<_MoneyT>
get_money(_MoneyT& __mon, bool __intl = false)
{ return { __mon, __intl }; }
template<typename _CharT, typename _Traits, typename _MoneyT>
basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Get_money<_MoneyT> __f)
{
typename basic_istream<_CharT, _Traits>::sentry __cerb(__is, false);
if (__cerb)
{
ios_base::iostate __err = ios_base::goodbit;
__try
{
typedef istreambuf_iterator<_CharT, _Traits> _Iter;
typedef money_get<_CharT, _Iter> _MoneyGet;
const _MoneyGet& __mg = use_facet<_MoneyGet>(__is.getloc());
__mg.get(_Iter(__is.rdbuf()), _Iter(), __f._M_intl,
__is, __err, __f._M_mon);
}
__catch(__cxxabiv1::__forced_unwind&)
{
__is._M_setstate(ios_base::badbit);
__throw_exception_again;
}
__catch(...)
{ __is._M_setstate(ios_base::badbit); }
if (__err)
__is.setstate(__err);
}
return __is;
}
template<typename _MoneyT>
struct _Put_money { const _MoneyT& _M_mon; bool _M_intl; };
/**
* @brief Extended manipulator for inserting money.
* @param __mon Either long double or a specialization of @c basic_string.
* @param __intl A bool indicating whether international format
* is to be used.
*
* Sent to a stream object, this manipulator inserts @a __mon.
*/
template<typename _MoneyT>
inline _Put_money<_MoneyT>
put_money(const _MoneyT& __mon, bool __intl = false)
{ return { __mon, __intl }; }
template<typename _CharT, typename _Traits, typename _MoneyT>
basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Put_money<_MoneyT> __f)
{
typename basic_ostream<_CharT, _Traits>::sentry __cerb(__os);
if (__cerb)
{
ios_base::iostate __err = ios_base::goodbit;
__try
{
typedef ostreambuf_iterator<_CharT, _Traits> _Iter;
typedef money_put<_CharT, _Iter> _MoneyPut;
const _MoneyPut& __mp = use_facet<_MoneyPut>(__os.getloc());
if (__mp.put(_Iter(__os.rdbuf()), __f._M_intl, __os,
__os.fill(), __f._M_mon).failed())
__err |= ios_base::badbit;
}
__catch(__cxxabiv1::__forced_unwind&)
{
__os._M_setstate(ios_base::badbit);
__throw_exception_again;
}
__catch(...)
{ __os._M_setstate(ios_base::badbit); }
if (__err)
__os.setstate(__err);
}
return __os;
}
#if __cplusplus > 201103L
#define __cpp_lib_quoted_string_io 201304
_GLIBCXX_END_NAMESPACE_VERSION
namespace __detail {
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @brief Struct for delimited strings.
*/
template<typename _String, typename _CharT>
struct _Quoted_string
{
static_assert(is_reference<_String>::value
|| is_pointer<_String>::value,
"String type must be pointer or reference");
_Quoted_string(_String __str, _CharT __del, _CharT __esc)
: _M_string(__str), _M_delim{__del}, _M_escape{__esc}
{ }
_Quoted_string&
operator=(_Quoted_string&) = delete;
_String _M_string;
_CharT _M_delim;
_CharT _M_escape;
};
/**
* @brief Inserter for quoted strings.
*
* _GLIBCXX_RESOLVE_LIB_DEFECTS
* DR 2344 quoted()'s interaction with padding is unclear
*/
template<typename _CharT, typename _Traits>
auto&
operator<<(std::basic_ostream<_CharT, _Traits>& __os,
const _Quoted_string<const _CharT*, _CharT>& __str)
{
std::basic_ostringstream<_CharT, _Traits> __ostr;
__ostr << __str._M_delim;
for (const _CharT* __c = __str._M_string; *__c; ++__c)
{
if (*__c == __str._M_delim || *__c == __str._M_escape)
__ostr << __str._M_escape;
__ostr << *__c;
}
__ostr << __str._M_delim;
return __os << __ostr.str();
}
/**
* @brief Inserter for quoted strings.
*
* _GLIBCXX_RESOLVE_LIB_DEFECTS
* DR 2344 quoted()'s interaction with padding is unclear
*/
template<typename _CharT, typename _Traits, typename _String>
auto&
operator<<(std::basic_ostream<_CharT, _Traits>& __os,
const _Quoted_string<_String, _CharT>& __str)
{
std::basic_ostringstream<_CharT, _Traits> __ostr;
__ostr << __str._M_delim;
for (auto& __c : __str._M_string)
{
if (__c == __str._M_delim || __c == __str._M_escape)
__ostr << __str._M_escape;
__ostr << __c;
}
__ostr << __str._M_delim;
return __os << __ostr.str();
}
/**
* @brief Extractor for delimited strings.
* The left and right delimiters can be different.
*/
template<typename _CharT, typename _Traits, typename _Alloc>
auto&
operator>>(std::basic_istream<_CharT, _Traits>& __is,
const _Quoted_string<basic_string<_CharT, _Traits, _Alloc>&,
_CharT>& __str)
{
_CharT __c;
__is >> __c;
if (!__is.good())
return __is;
if (__c != __str._M_delim)
{
__is.unget();
__is >> __str._M_string;
return __is;
}
__str._M_string.clear();
std::ios_base::fmtflags __flags
= __is.flags(__is.flags() & ~std::ios_base::skipws);
do
{
__is >> __c;
if (!__is.good())
break;
if (__c == __str._M_escape)
{
__is >> __c;
if (!__is.good())
break;
}
else if (__c == __str._M_delim)
break;
__str._M_string += __c;
}
while (true);
__is.setf(__flags);
return __is;
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace __detail
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @brief Manipulator for quoted strings.
* @param __str String to quote.
* @param __delim Character to quote string with.
* @param __escape Escape character to escape itself or quote character.
*/
template<typename _CharT>
inline auto
quoted(const _CharT* __string,
_CharT __delim = _CharT('"'), _CharT __escape = _CharT('\'))
{
return __detail::_Quoted_string<const _CharT*, _CharT>(__string, __delim,
__escape);
}
template<typename _CharT, typename _Traits, typename _Alloc>
inline auto
quoted(const basic_string<_CharT, _Traits, _Alloc>& __string,
_CharT __delim = _CharT('"'), _CharT __escape = _CharT('\'))
{
return __detail::_Quoted_string<
const basic_string<_CharT, _Traits, _Alloc>&, _CharT>(
__string, __delim, __escape);
}
template<typename _CharT, typename _Traits, typename _Alloc>
inline auto
quoted(basic_string<_CharT, _Traits, _Alloc>& __string,
_CharT __delim = _CharT('"'), _CharT __escape = _CharT('\'))
{
return __detail::_Quoted_string<
basic_string<_CharT, _Traits, _Alloc>&, _CharT>(
__string, __delim, __escape);
}
#endif // __cplusplus > 201103L
#endif // __cplusplus >= 201103L
// Inhibit implicit instantiations for required instantiations,
// which are defined via explicit instantiations elsewhere.
// NB: This syntax is a GNU extension.
#if _GLIBCXX_EXTERN_TEMPLATE
extern template ostream& operator<<(ostream&, _Setfill<char>);
extern template ostream& operator<<(ostream&, _Setiosflags);
extern template ostream& operator<<(ostream&, _Resetiosflags);
extern template ostream& operator<<(ostream&, _Setbase);
extern template ostream& operator<<(ostream&, _Setprecision);
extern template ostream& operator<<(ostream&, _Setw);
extern template istream& operator>>(istream&, _Setfill<char>);
extern template istream& operator>>(istream&, _Setiosflags);
extern template istream& operator>>(istream&, _Resetiosflags);
extern template istream& operator>>(istream&, _Setbase);
extern template istream& operator>>(istream&, _Setprecision);
extern template istream& operator>>(istream&, _Setw);
#ifdef _GLIBCXX_USE_WCHAR_T
extern template wostream& operator<<(wostream&, _Setfill<wchar_t>);
extern template wostream& operator<<(wostream&, _Setiosflags);
extern template wostream& operator<<(wostream&, _Resetiosflags);
extern template wostream& operator<<(wostream&, _Setbase);
extern template wostream& operator<<(wostream&, _Setprecision);
extern template wostream& operator<<(wostream&, _Setw);
extern template wistream& operator>>(wistream&, _Setfill<wchar_t>);
extern template wistream& operator>>(wistream&, _Setiosflags);
extern template wistream& operator>>(wistream&, _Resetiosflags);
extern template wistream& operator>>(wistream&, _Setbase);
extern template wistream& operator>>(wistream&, _Setprecision);
extern template wistream& operator>>(wistream&, _Setw);
#endif
#endif
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif /* _GLIBCXX_IOMANIP */
代码随便复制，要是不小心把缺省源改掉了，复制粘贴就行。
其他参考：https://www.cnblogs.com/lsgxeva/p/7696410.html