C++ 标准库之iomanip

istream & istream::get(char *, int, char = '\n');
istream & istream::getline(char *, int, char = '\n');
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

basefield

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。

#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;
}

运行结果：

 msvc 11.0 Visual Studio 2012  中iomanip头文件内容：

// iomanip standard header
#pragma once
#ifndef _IOMANIP_
#define _IOMANIP_
#ifndef RC_INVOKED
#include <istream>

#include <type_traits>

#include <xlocmon>
#include <xloctime>

#pragma pack(push,_CRT_PACKING)
#pragma warning(push,3)
#pragma push_macro("new")
#undef new

_STD_BEGIN
// TEMPLATE STRUCT _Fillobj
template<class _Elem>
struct _Fillobj
{    // store fill character
_Fillobj(_Elem _Ch)
: _Fill(_Ch)
{    // construct from fill character
}

_Elem _Fill;    // the fill character
};

// TEMPLATE FUNCTION setfill
template<class _Elem> inline
_Fillobj<_Elem> setfill(_Elem _Ch)
{    // return a _Fillobj manipulator
return (_Fillobj<_Elem>(_Ch));
}

template<class _Elem,
class _Traits,
class _Elem2> inline
basic_istream<_Elem, _Traits>&
operator>>(basic_istream<_Elem, _Traits>& _Istr,
const _Fillobj<_Elem2>& _Manip)
{    // set fill character in input stream
static_assert((is_same<_Elem, _Elem2>::value),
"wrong character type for setfill");

_Istr.fill(_Manip._Fill);
return (_Istr);
}

template<class _Elem,
class _Traits,
class _Elem2> inline
basic_ostream<_Elem, _Traits>&
operator<<(basic_ostream<_Elem, _Traits>& _Ostr,
const _Fillobj<_Elem2>& _Manip)
{    // set fill character in output stream
static_assert((is_same<_Elem, _Elem2>::value),
"wrong character type for setfill");

_Ostr.fill(_Manip._Fill);
return (_Ostr);
}

#if _HAS_CPP0X
// TEMPLATE STRUCT _Monobj
template<class _Money>
struct _Monobj
{    // store reference to monetary amount
_Monobj(_Money& _Val_arg, bool _Intl_arg)
: _Val(_Val_arg), _Intl(_Intl_arg)
{    // construct from monetary amount reference and int'l flag
}

_Money& _Val;    // the monetary amount reference
bool _Intl;        // international flag

private:
_Monobj& operator=(const _Monobj&);
};

// TEMPLATE FUNCTION get_money
template<class _Money> inline
_Monobj<_Money> get_money(_Money& _Val_arg,
bool _Intl_arg = false)
{    // return a _Monobj manipulator
return (_Monobj<_Money>(_Val_arg, _Intl_arg));
}

template<class _Elem,
class _Traits,
class _Money> inline
basic_istream<_Elem, _Traits>&
operator>>(basic_istream<_Elem, _Traits>& _Istr,
const _Monobj<_Money>& _Manip)
{    // get monetary amount from input stream
typedef basic_istream<_Elem, _Traits> _Myis;
typedef istreambuf_iterator<_Elem, _Traits> _Iter;
typedef money_get<_Elem, _Iter> _Mymget;

ios_base::iostate _State = ios_base::goodbit;
const typename _Myis::sentry _Ok(_Istr);

if (_Ok)
{    // state okay, extract monetary amount
const _Mymget& _Mget_fac = _USE(_Istr.getloc(), _Mymget);
_TRY_IO_BEGIN
_Mget_fac.get(_Iter(_Istr.rdbuf()), _Iter(0), _Manip._Intl,
_Istr, _State, _Manip._Val);
_CATCH_IO_(_Istr)
}

_Istr.setstate(_State);
return (_Istr);
}

// TEMPLATE FUNCTION put_money
template<class _Money> inline
_Monobj<const _Money>
put_money(const _Money& _Val_arg,
bool _Intl_arg = false)
{    // return a _Monobj manipulator
return (_Monobj<const _Money>(_Val_arg, _Intl_arg));
}

template<class _Elem,
class _Traits,
class _Money> inline
basic_ostream<_Elem, _Traits>&
operator<<(basic_ostream<_Elem, _Traits>& _Ostr,
const _Monobj<_Money>& _Manip)
{    // put monetary amount to output stream
typedef basic_ostream<_Elem, _Traits> _Myos;
typedef ostreambuf_iterator<_Elem, _Traits> _Iter;
typedef money_put<_Elem, _Iter> _Mymput;

ios_base::iostate _State = ios_base::goodbit;
const typename _Myos::sentry _Ok(_Ostr);

if (_Ok)
{    // state okay, insert monetary amount
const _Mymput& _Mput_fac = _USE(_Ostr.getloc(), _Mymput);
_TRY_IO_BEGIN
if (_Mput_fac.put(_Iter(_Ostr.rdbuf()), _Manip._Intl,
_Ostr, _Ostr.fill(), _Manip._Val).failed())
_State |= ios_base::badbit;
_CATCH_IO_(_Ostr)
}

_Ostr.setstate(_State);
return (_Ostr);
}

// TEMPLATE STRUCT _Timeobj
template<class _Elem>
struct _Timeobj
{    // store reference to tm object and format
_Timeobj(struct tm *_Tptr_arg, const _Elem *_Fmt_arg)
: _Tptr(_Tptr_arg), _Fmtfirst(_Fmt_arg)
{    // construct from tm pointer and format pointer
for (_Fmtlast = _Fmtfirst; *_Fmtlast != 0; ++_Fmtlast)
;    // find end of format string
}

struct tm *_Tptr;    // the tm struct pointer
const _Elem *_Fmtfirst;    // format string start
const _Elem *_Fmtlast;    // format string end
};

// TEMPLATE FUNCTION get_time
template<class _Elem> inline
_Timeobj<_Elem>
get_time(struct tm *_Tptr_arg, const _Elem *_Fmt_arg)
{    // return a _Timeobj manipulator
return (_Timeobj<_Elem>(_Tptr_arg, _Fmt_arg));
}

template<class _Elem,
class _Traits,
class _Elem2> inline
basic_istream<_Elem, _Traits>&
operator>>(basic_istream<_Elem, _Traits>& _Istr,
const _Timeobj<_Elem2>& _Manip)
{    // get time information from input stream
typedef basic_istream<_Elem, _Traits> _Myis;
typedef istreambuf_iterator<_Elem, _Traits> _Iter;
typedef time_get<_Elem2, _Iter> _Mytget;

static_assert((is_same<_Elem, _Elem2>::value),
"wrong character type for get_time");

ios_base::iostate _State = ios_base::goodbit;
const typename _Myis::sentry _Ok(_Istr);

if (_Ok)
{    // state okay, extract time amounts
const _Mytget& _Tget_fac = _USE(_Istr.getloc(), _Mytget);
_TRY_IO_BEGIN
_Tget_fac.get(_Iter(_Istr.rdbuf()), _Iter(0), _Istr, _State,
_Manip._Tptr, _Manip._Fmtfirst, _Manip._Fmtlast);
_CATCH_IO_(_Istr)
}

_Istr.setstate(_State);
return (_Istr);
}

// TEMPLATE FUNCTION put_time
template<class _Elem> inline
_Timeobj<_Elem>
put_time(struct tm *_Tptr_arg, const _Elem *_Fmt_arg)
{    // return a _Timeobj manipulator
return (_Timeobj<_Elem>(_Tptr_arg, _Fmt_arg));
}

template<class _Elem,
class _Traits,
class _Elem2> inline
basic_ostream<_Elem, _Traits>&
operator<<(basic_ostream<_Elem, _Traits>& _Ostr,
const _Timeobj<_Elem2>& _Manip)
{    // put time information to output stream
typedef basic_ostream<_Elem, _Traits> _Myos;
typedef ostreambuf_iterator<_Elem, _Traits> _Iter;
typedef time_put<_Elem2, _Iter> _Mytput;

static_assert((is_same<_Elem, _Elem2>::value),
"wrong character type for put_time");

ios_base::iostate _State = ios_base::goodbit;
const typename _Myos::sentry _Ok(_Ostr);

if (_Ok)
{    // state okay, insert monetary amount
const _Mytput& _Tput_fac = _USE(_Ostr.getloc(), _Mytput);
_TRY_IO_BEGIN
if (_Tput_fac.put(_Iter(_Ostr.rdbuf()), _Ostr, _Ostr.fill(),
_Manip._Tptr, _Manip._Fmtfirst, _Manip._Fmtlast).failed())
_State |= ios_base::badbit;
_CATCH_IO_(_Ostr)
}

_Ostr.setstate(_State);
return (_Ostr);
}
#endif /* _HAS_CPP0X */

// TEMPLATE STRUCT _Smanip
template<class _Arg>
struct _Smanip
{    // store function pointer and argument value
_Smanip(void (__cdecl *_Left)(ios_base&, _Arg), _Arg _Val)
: _Pfun(_Left), _Manarg(_Val)
{    // construct from function pointer and argument value
}

void (__cdecl *_Pfun)(ios_base&, _Arg);    // the function pointer
_Arg _Manarg;    // the argument value
};

template<class _Elem,
class _Traits,
class _Arg> inline
basic_istream<_Elem, _Traits>& operator>>(
basic_istream<_Elem, _Traits>& _Istr, const _Smanip<_Arg>& _Manip)
{    // extract by calling function with input stream and argument
(*_Manip._Pfun)(_Istr, _Manip._Manarg);
return (_Istr);
}

template<class _Elem,
class _Traits,
class _Arg> inline
basic_ostream<_Elem, _Traits>& operator<<(
basic_ostream<_Elem, _Traits>& _Ostr, const _Smanip<_Arg>& _Manip)
{    // insert by calling function with output stream and argument
(*_Manip._Pfun)(_Ostr, _Manip._Manarg);
return (_Ostr);
}

// INSTANTIATIONS
_MRTIMP2 _Smanip<ios_base::fmtflags> __cdecl resetiosflags(ios_base::fmtflags);
_MRTIMP2 _Smanip<ios_base::fmtflags> __cdecl setiosflags(ios_base::fmtflags);
_MRTIMP2 _Smanip<int> __cdecl setbase(int);
_MRTIMP2 _Smanip<streamsize> __cdecl setprecision(streamsize);
_MRTIMP2 _Smanip<streamsize> __cdecl setw(streamsize);
_STD_END
#pragma pop_macro("new")
#pragma warning(pop)
#pragma pack(pop)
#endif /* RC_INVOKED */
#endif /* _IOMANIP_ */

/*
* Copyright (c) 1992-2012 by P.J. Plauger.  ALL RIGHTS RESERVED.
* Consult your license regarding permissions and restrictions.
V6.00:0009 */

如何确定VS编译器版本

_MSC_VER是MSVC编译器的内置宏，定义了编译器的版本，_MSC_VER 值对应版本关系
MSVC++ 11.0 _MSC_VER = 1700 (Visual Studio 2012)
MSVC++ 10.0 _MSC_VER = 1600 (Visual Studio 2010)
MSVC++ 9.0 _MSC_VER = 1500 (Visual Studio 2008)
MSVC++ 8.0 _MSC_VER = 1400 (Visual Studio 2005)
MSVC++ 7.1 _MSC_VER = 1310 (Visual Studio 2003)
MSVC++ 7.0 _MSC_VER = 1300 (Visual Studio 2002)
MSVC++ 6.0 _MSC_VER = 1200
MSVC++ 5.0 _MSC_VER = 1100

example：
#if (_MSC_VER == 1300) //vc7
#import "acax16ENU.tlb" no_implementation raw_interfaces_only named_guids
#elif (_MSC_VER == 1200) //vc6
#import "acad.tlb" no_implementation raw_interfaces_only named_guids
#elif (_MSC_VER == 1400) //vc8
#import "acax17ENU.tlb" no_implementation raw_interfaces_only named_guids
#elif (_MSC_VER == 1500) //vc9
#import "acax18ENU.tlb" no_implementation raw_interfaces_only named_guids
#endif

在程序中加入_MSC_VER宏可以根据编译器版本让编译器选择性地编译一段程序。例如一个版本编译器产生的lib文件可能不能被另一个版
本的编译器调用，那么在开发应用程序的时候，在该程序的lib调用库中放入多个版本编译器产生的lib文件。在程序中加入_MSC_VER宏
，编译器就能够在调用的时根据其版本自动选择可以链接的lib库版本，如下所示。
#if _MSC_VER >= 1400 // for vc8, or vc9
#ifdef _DEBUG
#pragma comment( lib, "SomeLib-vc8-d.lib" )
#else if
#pragma comment( lib, "SomeLib-vc8-r.lib" )
#endif
#else if _MSC_VER >= 1310 // for vc71
#ifdef _DEBUG
#pragma comment( lib, "SomeLib-vc71-d.lib" )
#else if
#pragma comment( lib, "SomeLib-vc71-r.lib" )
#endif
#else if _MSC_VER >=1200 // for vc6
#ifdef _DEBUG
#pragma comment( lib, "SomeLib-vc6-d.lib" )
#else if
#pragma comment( lib, "SomeLib-vc6-r.lib" )
#endif
#endif