STL(10)之advance組函數源碼

1.函數說明：

<span style="font-size:18px;"> /**
   *  @brief A generalization of pointer arithmetic.
   *  @param  __i  An input iterator.
   *  @param  __n  The @a delta by which to change @p __i.
   *  @return  Nothing.
   *
   *  This increments @p i by @p n.  For bidirectional and random access
   *  iterators, @p __n may be negative, in which case @p __i is decremented.
   *
   *  For random access iterators, this uses their @c + and @c - operations
   *  and are constant time.  For other %iterator classes they are linear time.
  */</span>

2.For InputIterator:

  template<typename _InputIterator, typename _Distance>
    inline void
    __advance(_InputIterator& __i, _Distance __n, input_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      _GLIBCXX_DEBUG_ASSERT(__n >= 0);
      while (__n--)
	++__i;
    }

 

3.For  BidirectionIterator:

  template<typename _BidirectionalIterator, typename _Distance>
    inline void
    __advance(_BidirectionalIterator& __i, _Distance __n,
	      bidirectional_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      if (__n > 0)
        while (__n--)
	  ++__i;
      else
        while (__n++)
	  --__i;
    }

 

4.For RandomIterator:

  template<typename _RandomAccessIterator, typename _Distance>
    inline void
    __advance(_RandomAccessIterator& __i, _Distance __n,
              random_access_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      __i += __n;
    }

5.提供給用戶的接口實現：

  template<typename _InputIterator, typename _Distance>
    inline void
    advance(_InputIterator& __i, _Distance __n)
    {
      // concept requirements -- taken care of in __advance
      typename iterator_traits<_InputIterator>::difference_type __d = __n;
      std::__advance(__i, __d, std::__iterator_category(__i));
    }