分类

Instead of being defined by specific types, each category of iterator is defined by the operations that can be performed on it.

Iterator category	Operations and storage requirement
	write	read	increment		decrement	random access	contiguous storage
	write	read	without multiple passes	with multiple passes	decrement	random access	contiguous storage
LegacyIterator			Required
LegacyOutputIterator	Required		Required
LegacyInputIterator (mutable if supports write operation)		Required	Required
LegacyForwardIterator (also satisfies LegacyInputIterator)		Required	Required	Required
LegacyBidirectionalIterator (also satisfies LegacyForwardIterator)		Required	Required	Required	Required
LegacyRandomAccessIterator (also satisfies LegacyBidirectionalIterator)		Required	Required	Required	Required	Required
LegacyContiguousIterator^[1] (also satisfies LegacyRandomAccessIterator)		Required	Required	Required	Required	Required	Required

iterators