[流解析 vs 2005]ios_base
vs 2005中ios_base继承自_Iosb<int>，主要提供流状态控制、格式控制、本地化等方面支持。
1、类型和数据定义
class ios_base : public _Iosb<int>
{
public:
// 预定义类型
_BITMASK(_Fmtflags, fmtflags); // 其实是typedef int fmtflags 第一个方便理解
_BITMASK(_Iostate, iostate);
_BITMASK(_Openmode, openmode);
_BITMASK(_Seekdir, seekdir);
typedef std::streamoff streamoff;
typedef std::streampos streampos;
enum event
{ // constants for ios events
erase_event, imbue_event, copyfmt_event};
typedef void (__CLRCALL_OR_CDECL *event_callback)(event, ios_base&, int);
class failure // 用于抛出异常。
: public runtime_error
{
public:
explicit failure(const string &_Message)
: runtime_error(_Message) {}
virtual ~failure() throw () {}
#if !_HAS_EXCEPTIONS
protected:
virtual void _Doraise() const // exception中有相关信息
{ // report the exception
_RAISE(*this);
}
#endif /* _HAS_EXCEPTIONS */
};
class Init // 作用？
{ // controller for standard-stream initialization
public:
Init() { _Init_ctor(this); }
~Init() { _Init_dtor(this); }
private:
static void __cdecl _Init_ctor(Init *); // 位于iostream.cpp中
static void __cdecl _Init_dtor(Init *); // 位于iostream.cpp中
static int& __cdecl _Init_cnt_func(); // 位于iostream.cpp中
static int _Init_cnt; // net constructions - destructions
};
// ...
private:
iostate _Mystate; // stream state
iostate _Except; // exception mask
fmtflags _Fmtfl; // format flags
streamsize _Prec; // field precision
streamsize _Wide; // field width
_Iosarray *_Arr; // ?? pointer to first node of long/pointer array
_Fnarray *_Calls; // ?? pointer to first node of call list
locale *_Ploc; // pointer to locale
static int _Index; // ?? source of unique indexes for long/pointer array
static bool _Sync; // ?? C/C++ synchronization flag (ignored)
};
其中:_Mystate是流状态，_Except是异常掩码，用于标识在流在哪些状态下抛出异常；_Fmtfl是格式；_Prec是精度；_Wide是宽度；_Arr 和 _Calls暂不明白； Ploc是本地化相关信息；_Index 和 _Sync 暂不明白。
二、流状态操作：
// 流状态操作
void clear(iostate _State, bool _Reraise) // 第二个参数表示是否重新抛出异常
{ // set state, possibly reraise exception
_Mystate = (iostate)(_State & _Statmask);
if ((_Mystate & _Except) == 0)
;
else if (_Reraise)
_RERAISE;
else if (_Mystate & _Except & badbit)
_THROW_NCEE(failure, "ios_base::badbit set");
else if (_Mystate & _Except & failbit)
_THROW_NCEE(failure, "ios_base::failbit set");
else
_THROW_NCEE(failure, "ios_base::eofbit set");
}
void clear(iostate _State = goodbit)
{
clear(_State, false);
}
iostate rdstate() const; // return (_Mystate);
void setstate(iostate _State)
{ // merge in state argument
if (_State != goodbit)
clear((iostate)((int)rdstate() | (int)_State), false);
}
bool good() const; // return (rdstate() == goodbit);
bool eof() const; // return ((int)rdstate() & (int)eofbit);
bool fail() const; // return (((int)rdstate() & ((int)badbit | (int)failbit)) != 0);
bool bad() const; // return (((int)rdstate() & (int)badbit) != 0);
// 异常掩码：用于确定哪些状态下抛出异常
iostate exceptions() const; // return (_Except);
void exceptions(iostate _Newexcept)
{
_Except = (iostate)((int)_Newexcept & (int)_Statmask);
clear(_Mystate);
}
三、流格式化标志操作：
// 流格式化标志操作
fmtflags flags() const // return (_Fmtfl);
fmtflags flags(fmtflags _Newfmtflags)
{ // set format flags to argument
fmtflags _Oldfmtflags = _Fmtfl;
_Fmtfl = (fmtflags)((int)_Newfmtflags & (int)_Fmtmask);
return (_Oldfmtflags);
}
fmtflags setf(fmtflags _Newfmtflags, fmtflags _Mask)
{ // merge in format flags argument under mask argument
ios_base::fmtflags _Oldfmtflags = _Fmtfl;
_Fmtfl = (fmtflags)(((int)_Fmtfl & (int)~_Mask)
| ((int)_Newfmtflags & (int)_Mask & (int)_Fmtmask));
return (_Oldfmtflags);
}
void unsetf(fmtflags _Mask)
{ // clear format flags under mask argument
_Fmtfl = (fmtflags)((int)_Fmtfl & (int)~_Mask);
}
streamsize precision(streamsize _Newprecision)
{ // set precision to argument
streamsize _Oldprecision = _Prec;
_Prec = _Newprecision;
return (_Oldprecision);
}
streamsize width() const; // return (_Wide);
streamsize width(streamsize _Newwidth)
{ // set width to argument
streamsize _Oldwidth = _Wide;
_Wide = _Newwidth;
return (_Oldwidth);
}
四、本地化相关处理：
// 本地化相关处理
locale getloc() const
{ // get locale
return (*_Ploc);
}
locale imbue(const locale& _Loc)
{ // set locale to argument
locale _Oldlocale = *_Ploc;
*_Ploc = _Loc;
_Callfns(imbue_event); // _Calls成员变量中维护了一系列函数
return (_Oldlocale);
}
五、
五、成员变量_Arr相关处理：
struct _Iosarray
{ // list element for open-ended sparse array of longs/pointers
public:
_Iosarray(int _Idx, _Iosarray *_Link)
: _Next(_Link), _Index(_Idx), _Lo(0), _Vp(0)
{ // construct node for index _Idx and link it in
}
_Iosarray *_Next; // pointer to next node
int _Index; // index of this node
long _Lo; // stored long value
void *_Vp; // stored pointer value
};
long& iword(int _Idx)
{ // return reference to long element
return (_Findarr(_Idx)._Lo);
}
void *& pword(int _Idx)
{ // return reference to pointer element
return (_Findarr(_Idx)._Vp);
}
_Iosarray& _Findarr(int _Idx)
{ // locate or make a variable array element
_Iosarray *_Ptr, *_Q;
for (_Ptr = _Arr, _Q = 0; _Ptr != 0; _Ptr = _Ptr->_Next)
if (_Ptr->_Index == _Idx)
return (*_Ptr); // found element, return it
else if (_Q == 0 && _Ptr->_Lo == 0 && _Ptr->_Vp == 0)
_Q = _Ptr; // found recycling candidate
if (_Q != 0)
{ // recycle existing element
_Q->_Index = _Idx;
return (*_Q);
}
_Arr = _NEW_CRT _Iosarray(_Idx, _Arr); // make a new element
return (*_Arr);
}
六、成员变量_Calls处理：
struct _Fnarray
{ // list element for open-ended sparse array of event handlers
_Fnarray(int _Idx, event_callback _Pnew, _Fnarray *_Link)
: _Next(_Link), _Index(_Idx), _Pfn(_Pnew)
{ // construct node for index _Idx and link it in
}
_Fnarray *_Next; // pointer to next node
int _Index; // index of this node
event_callback _Pfn; // pointer to event handler
};
void register_callback(event_callback _Pfn, int _Idx)
{ // register event handler
_Calls = _NEW_CRT _Fnarray(_Idx, _Pfn, _Calls);
}
七、运算符重载：
ios_base& operator=(const ios_base& _Right)
{ // assign state and format stuff from _Right
if (this != &_Right)
{ // worth doing
_Mystate = _Right._Mystate;
copyfmt(_Right);
}
return (*this);
}
operator void *() const; // eg: if(cin)
bool operator!() const; // eg: if(!cin)