istream_iterator的自增

istream_iterator的自增

 

  // TEMPLATE CLASS istream_iterator
template<class _Ty,
 class _Elem = char,
 class _Traits = char_traits<_Elem>,
 class _Diff = ptrdiff_t>
 class istream_iterator
  : public iterator<input_iterator_tag, _Ty, _Diff,
   const _Ty *, const _Ty&>
 { // wrap _Ty extracts from input stream as input iterator
 typedef istream_iterator<_Ty, _Elem, _Traits, _Diff> _Myt;
public:
 typedef _Elem char_type;
 typedef _Traits traits_type;
 typedef basic_istream<_Elem, _Traits> istream_type;

#if _SECURE_SCL
 typedef _Range_checked_iterator_tag _Checked_iterator_category;
#endif

 istream_iterator()
  : _Myistr(0)
  { // construct singular iterator
  }

 istream_iterator(istream_type& _Istr)
  : _Myistr(&_Istr)
  { // construct with input stream
  _Getval();
  }

 const _Ty& operator*() const
  { // return designated value

 #if _HAS_ITERATOR_DEBUGGING
  if (_Myistr == 0)
   {
   _DEBUG_ERROR("istream_iterator is not dereferencable");
   _SCL_SECURE_OUT_OF_RANGE;
   }
 #else
  _SCL_SECURE_VALIDATE_RANGE(_Myistr != 0);
 #endif /* _HAS_ITERATOR_DEBUGGING */

  return (_Myval);
  }

 const _Ty *operator->() const
  { // return pointer to class object
  return (&**this);
  }

 _Myt& operator++()
  { // preincrement

 #if _HAS_ITERATOR_DEBUGGING
  if (_Myistr == 0)
   {
   _DEBUG_ERROR("istream_iterator is not incrementable");
   _SCL_SECURE_OUT_OF_RANGE;
   }
 #else
  _SCL_SECURE_VALIDATE_RANGE(_Myistr != 0);
 #endif /* _HAS_ITERATOR_DEBUGGING */

  _Getval();
  return (*this);
  }

 _Myt operator++(int)
  { // postincrement
  _Myt _Tmp = *this;
  ++*this;
  return (_Tmp);
  }

 bool _Equal(const _Myt& _Right) const
  { // test for iterator equality
  return (_Myistr == _Right._Myistr);
  }

protected:
 void _Getval()
  { // get a _Ty value if possible
  if (_Myistr != 0 && !(*_Myistr >> _Myval))
   _Myistr = 0;
  }

 static void _Xran()
  { // report an out_of_range error
  _THROW(out_of_range, "invalid istream_iterator");
  }

 istream_type *_Myistr; // pointer to input stream
 _Ty _Myval; // lookahead value (valid if _Myistr is not null)
 };

  // istream_iterator TEMPLATE OPERATORS
template<class _Ty,
 class _Elem,
 class _Traits,
 class _Diff> inline
 bool operator==(
  const istream_iterator<_Ty, _Elem, _Traits, _Diff>& _Left,
  const istream_iterator<_Ty, _Elem, _Traits, _Diff>& _Right)
 { // test for istream_iterator equality
 return (_Left._Equal(_Right));
 }

template<class _Ty,
 class _Elem,
 class _Traits,
 class _Diff> inline
 bool operator!=(
  const istream_iterator<_Ty, _Elem, _Traits, _Diff>& _Left,
  const istream_iterator<_Ty, _Elem, _Traits, _Diff>& _Right)
 { // test for istream_iterator inequality
 return (!(_Left == _Right));
 }

红色部分就是重点了，其实这种迭代器不能自增，只是不断把流中的元素放到自己所存的值里，当到达流末尾时，直接将判断指针设为0。