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Question pertaining to <xiosbase>

May 20, 2013 at 10:42am
base evil (2)
While using Microsoft Visual Studio 2010, there's a class _Iosb within <xiosbase>

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  // TEMPLATE CLASS _Iosb
template<class _Dummy>
	class _Iosb
	{	// define templatized bitmask/enumerated types, instantiate on demand
public:
	enum _Dummy_enum {_Dummy_enum_val = 1};	// don't ask
	enum _Fmtflags
		{	// constants for formatting options
		_Fmtmask = 0xffff, _Fmtzero = 0};

	static const _Fmtflags skipws = (_Fmtflags)_IOSskipws;
	static const _Fmtflags unitbuf = (_Fmtflags)_IOSunitbuf;
	static const _Fmtflags uppercase = (_Fmtflags)_IOSuppercase;
	static const _Fmtflags showbase = (_Fmtflags)_IOSshowbase;
	static const _Fmtflags showpoint = (_Fmtflags)_IOSshowpoint;
	static const _Fmtflags showpos = (_Fmtflags)_IOSshowpos;
	static const _Fmtflags left = (_Fmtflags)_IOSleft;
	static const _Fmtflags right = (_Fmtflags)_IOSright;
	static const _Fmtflags internal = (_Fmtflags)_IOSinternal;
	static const _Fmtflags dec = (_Fmtflags)_IOSdec;
	static const _Fmtflags oct = (_Fmtflags)_IOSoct;
	static const _Fmtflags hex = (_Fmtflags)_IOShex;
	static const _Fmtflags scientific = (_Fmtflags)_IOSscientific;
	static const _Fmtflags fixed = (_Fmtflags)_IOSfixed;

	static const _Fmtflags hexfloat =
		(_Fmtflags)_IOShexfloat;	// added with TR1/

	static const _Fmtflags boolalpha = (_Fmtflags)_IOSboolalpha;
	static const _Fmtflags _Stdio = (_Fmtflags)_IOS_Stdio;
	static const _Fmtflags adjustfield = (_Fmtflags)(_IOSleft
		| _IOSright | _IOSinternal);
	static const _Fmtflags basefield = (_Fmtflags)(_IOSdec
		| _IOSoct | _IOShex);
	static const _Fmtflags floatfield = (_Fmtflags)(_IOSscientific
		| _IOSfixed);

	enum _Iostate
		{	// constants for stream states
		_Statmask = 0x17};

	static const _Iostate goodbit = (_Iostate)0x0;
	static const _Iostate eofbit = (_Iostate)0x1;
	static const _Iostate failbit = (_Iostate)0x2;
	static const _Iostate badbit = (_Iostate)0x4;
	static const _Iostate _Hardfail = (_Iostate)0x10;

	enum _Openmode
		{	// constants for file opening options
		_Openmask = 0xff};

	static const _Openmode in = (_Openmode)0x01;
	static const _Openmode out = (_Openmode)0x02;
	static const _Openmode ate = (_Openmode)0x04;
	static const _Openmode app = (_Openmode)0x08;
	static const _Openmode trunc = (_Openmode)0x10;
	static const _Openmode _Nocreate = (_Openmode)_IOS_Nocreate;
	static const _Openmode _Noreplace = (_Openmode)_IOS_Noreplace;
	static const _Openmode binary = (_Openmode)_IOSbinary;

	enum _Seekdir
		{	// constants for file positioning options
		_Seekmask = 0x3};

	static const _Seekdir beg = (_Seekdir)0;
	static const _Seekdir cur = (_Seekdir)1;
	static const _Seekdir end = (_Seekdir)2;

	enum
		{	// constant for default file opening protection
		_Openprot = _OPENPROT};
	};


The class itself is pretty easy to understand, but after the class the following lines of code are present-

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template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::skipws;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::unitbuf;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::uppercase;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::showbase;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::showpoint;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::showpos;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::left;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::right;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::internal;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::dec;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::oct;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::hex;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::scientific;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::fixed;

template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags
		_Iosb<_Dummy>::hexfloat;	// added with TR1

template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::boolalpha;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::_Stdio;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::adjustfield;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::basefield;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::floatfield;

template<class _Dummy>
	const typename _Iosb<_Dummy>::_Iostate _Iosb<_Dummy>::goodbit;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Iostate _Iosb<_Dummy>::eofbit;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Iostate _Iosb<_Dummy>::failbit;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Iostate _Iosb<_Dummy>::badbit;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Iostate _Iosb<_Dummy>::_Hardfail;

template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::in;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::out;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::ate;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::app;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::trunc;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::_Nocreate;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::_Noreplace;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Openmode _Iosb<_Dummy>::binary;

template<class _Dummy>
	const typename _Iosb<_Dummy>::_Seekdir _Iosb<_Dummy>::beg;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Seekdir _Iosb<_Dummy>::cur;
template<class _Dummy>
	const typename _Iosb<_Dummy>::_Seekdir _Iosb<_Dummy>::end;


What do these lines of code do?

P.S. - I am pretty new to programming and this forum, so if this topic is in the wrong subforum(?) please forgive me.

Thanks,
base evil.
Last edited on May 20, 2013 at 10:43am
May 20, 2013 at 3:29pm
MiiNiPaa (8886)
Judging from underscore followed by capital letter, this is internal class used by implementation and does not intendet to be used by end-user. Looks like it is defines flags you usually access as ios::in, ios::out, ios::ate and others.
May 20, 2013 at 4:50pm
base evil (2)
Sorry, I did not word my question properly-

Revised question-

Isn't the definition in the class?(See the first block of code.)

Correct me if I am wrong but isn't the first block Creating the flags?

Then the second block is referring to them, with their type ("_Iosb<_Dummy>") in front? (const typename className::Enum1 className::ObjectWithTypeEnum1;)

The last part of the line "className::ObjectWithTypeEnum1" is referring to the flags created in the class.


As far as I know you don't refer to objects with their type in front of them.
Last edited on May 20, 2013 at 4:53pm
May 20, 2013 at 10:38pm
andywestken (4094)
Edit: On re-reading, the post I thought might be interesting (now below), I'm not so sure it's interesting.

- The static const values are being declared and initialized inside the class, but not defined.

- The lines after the class are then defining them but not re-initializing them.

And all these members are enum value (i.e. some sort of integer, depending on what the compiler choses to use.)

Andy

This post might be of interest: Not so interesting post

static variable in the class declaration or definition?
http://stackoverflow.com/questions/11178434/static-variable-in-the-class-declaration-or-definition
Last edited on May 21, 2013 at 12:08am
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