[流解析 vs 2005]basic_ios

basic_ios定义出“与字符类型及其相应字符特性相关”的stream class共同属性，其中包括stream所用的缓冲器。

1、类型定义

// _Elem表示字符类型，可能是char或wchar_t
// _Traits是字符特性类型，默认有char_traits<char> 和 char_traits<wchar_t>
template<class _Elem, class _Traits>
class basic_ios : public ios_base
{	// base class for basic_istream/basic_ostream
public:
	typedef basic_ios<_Elem, _Traits> _Myt; 
	typedef basic_ostream<_Elem, _Traits> _Myos;
	typedef basic_streambuf<_Elem, _Traits> _Mysb;
	typedef ctype<_Elem> _Ctype;
	typedef _Elem char_type;
	typedef _Traits traits_type;
	typedef typename _Traits::int_type int_type;
	typedef typename _Traits::pos_type pos_type;
	typedef typename _Traits::off_type off_type;
	// ...

private:
	_Mysb *_Mystrbuf;	// pointer to stream buffer
	_Myos *_Tiestr;		// pointer to tied output stream
	_Elem _Fillch;		// the fill character
}
template class basic_ios<char, char_traits<char> >;
template class basic_ios<wchar_t, char_traits<wchar_t> >;

_Mystrbuf是流缓冲区指针，_Tiestr是关联的输出流指针，_Fillch是填充字符。

二、构造函数

public:
	explicit basic_ios(_Mysb *_Strbuf)
	{	// construct from stream buffer pointer
		init(_Strbuf);
	}

	virtual ~basic_ios()
	{	// destroy the object
	}

protected:
	void init(_Mysb *_Strbuf = 0, bool _Isstd = false)
	{	// initialize with stream buffer pointer
		_Init();	// initialize ios_base
		_Mystrbuf = _Strbuf;
		_Tiestr = 0;
		_Fillch = widen(' ');

		if (_Mystrbuf == 0)
			setstate(badbit);

		if (_Isstd)
			_Addstd(this);	// special handling for standard streams
		else
			_Stdstr = 0;
	}

	basic_ios()
	{	// default constructor, do nothing
	}

private:
	basic_ios(const _Myt&);	// not defined
	_Myt& operator=(const _Myt&);	// not defined

可见，basic_ios不支持复制构造，而且也只能从派生类中调用其构造函数。唯一的显示构造函数，要求传入的参数是basic_streambuf<_Elem, _Traits>类型的流缓冲区指针。 basic_ios也不支持赋值。

 

三、操作：清除流状态、设置流状态、拷贝流标志、返回或设置流缓冲区指针、设置本地化相关信息、返回或设置填充字符、字符转换

	// Clears all error flags.
	void clear(iostate _State = goodbit, bool _Reraise = false)
	{	// set state, possibly reraise exception
		ios_base::clear((iostate)(_Mystrbuf == 0
			? (int)_State | (int)badbit : (int)_State), _Reraise);
	}
	void clear(io_state _State)		// 
	{	// set state to _State
		clear((iostate)_State);
	}

	// Sets additional flags.
	void setstate(iostate _State, bool _Reraise = false)
	{	// merge _State into state, possible reraise exception
		if (_State != goodbit)
			clear((iostate)((int)rdstate() | (int)_State), _Reraise);
	}
	void setstate(io_state _State)
	{	// merge _State into state
		setstate((iostate)_State);
	}

	// Copies flags from one stream to another.
	_Myt& copyfmt(const _Myt& _Right)
	{	// copy format parameters
		_Tiestr = _Right.tie();
		_Fillch = _Right.fill();
		ios_base::copyfmt(_Right);
		return (*this);
	}

	// Ensures that one stream is processed before another stream.
	_Myos * tie() const
	{	// return tie pointer
		return (_Tiestr);
	}
	_Myos * tie(_Myos *_Newtie)
	{	// set tie pointer
		_Myos *_Oldtie = _Tiestr;
		_Tiestr = _Newtie;
		return (_Oldtie);
	}

	// 返回或设置流缓冲区指针
	_Mysb * rdbuf() const
	{	// return stream buffer pointer
		return (_Mystrbuf);
	}
	_Mysb * rdbuf(_Mysb *_Strbuf)
	{	// set stream buffer pointer
		_Mysb *_Oldstrbuf = _Mystrbuf;
		_Mystrbuf = _Strbuf;
		clear();
		return (_Oldstrbuf);
	}

	// 设置本地化相关信息
	locale imbue(const locale& _Loc)
	{	// set locale to argument
		locale _Oldlocale = ios_base::imbue(_Loc);
		if (rdbuf() != 0)
			rdbuf()->pubimbue(_Loc);
		return (_Oldlocale);
	}

	// 返回或设置填充字符
	_Elem fill() const
	{	// return fill character
		return (_Fillch);
	}
	_Elem fill(_Elem _Newfill)
	{	// set fill character
		_Elem _Oldfill = _Fillch;
		_Fillch = _Newfill;
		return (_Oldfill);
	}

	// 字符转换
	char narrow(_Elem _Ch, char _Dflt = '\0') const
	{	// convert _Ch to byte using imbued locale
		const _Ctype& _Ctype_fac = _USE(getloc(), _Ctype);
		return (_Ctype_fac.narrow(_Ch, _Dflt));
	}
	_Elem widen(char _Byte) const
	{	// convert _Byte to character using imbued locale
		const _Ctype& _Ctype_fac = _USE(getloc(), _Ctype);
		return (_Ctype_fac.widen(_Byte));
	}