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素颜马尾好姑娘i 2022-07-12 08:29 160阅读 0赞

1. 通过迭代器萃取类型：

/\*\* \* This class does nothing but define nested typedefs. The general \* version simply "forwards" the nested typedefs from the Iterator \* argument. Specialized versions for pointers and pointers-to-const \* provide tighter, more correct semantics. \*/ template<typename \_Iterator> struct iterator\_traits \{ typedef typename \_Iterator::iterator\_category iterator\_category; typedef typename \_Iterator::value\_type value\_type; typedef typename \_Iterator::difference\_type difference\_type; typedef typename \_Iterator::pointer pointer; typedef typename \_Iterator::reference reference; \}; template<typename \_Tp> struct iterator\_traits<\_Tp\*> \{ typedef random\_access\_iterator\_tag iterator\_category; typedef \_Tp value\_type; typedef ptrdiff\_t difference\_type; typedef \_Tp\* pointer; typedef \_Tp& reference; \}; template<typename \_Tp> struct iterator\_traits<const \_Tp\*> \{ typedef random\_access\_iterator\_tag iterator\_category; typedef \_Tp value\_type; typedef ptrdiff\_t difference\_type; typedef const \_Tp\* pointer; typedef const \_Tp& reference; \};

通过访问iterator\_traits<itr>::value\_type可以返回itr所指向的类型。

不过要在自己的itr中定义：

\_Iterator::iterator\_category  
\_Iterator::value\_type  
\_Iterator::difference\_type  
\_Iterator::pointer  
\_Iterator::reference

后面两个是特化版本。

下面是迭代器的定义，内含需自己定义的类型：

/\*\* \* @brief Common %iterator class. \* \* This class does nothing but define nested typedefs. %Iterator classes \* can inherit from this class to save some work. The typedefs are then \* used in specializations and overloading. \* \* In particular, there are no default implementations of requirements \* such as @c operator++ and the like. (How could there be?) \*/ template<typename \_Category, typename \_Tp, typename \_Distance = ptrdiff\_t, typename \_Pointer = \_Tp\*, typename \_Reference = \_Tp&> struct iterator \{ /// One of the @link iterator\_tags tag types@endlink. typedef \_Category iterator\_category; /// The type "pointed to" by the iterator. typedef \_Tp value\_type; /// Distance between iterators is represented as this type. typedef \_Distance difference\_type; /// This type represents a pointer-to-value\_type. typedef \_Pointer pointer; /// This type represents a reference-to-value\_type. typedef \_Reference reference; \};

2. 迭代器的类型

/\*\* \* @defgroup iterators Iterators \* These are empty types, used to distinguish different iterators. The \* distinction is not made by what they contain, but simply by what they \* are. Different underlying algorithms can then be used based on the \* different operations supported by different iterator types. \*/ //@\{ /// Marking input iterators. struct input\_iterator\_tag \{ \}; /// Marking output iterators. struct output\_iterator\_tag \{ \}; /// Forward iterators support a superset of input iterator operations. struct forward\_iterator\_tag : public input\_iterator\_tag \{ \}; /// Bidirectional iterators support a superset of forward iterator /// operations. struct bidirectional\_iterator\_tag : public forward\_iterator\_tag \{ \}; /// Random-access iterators support a superset of bidirectional iterator /// operations. struct random\_access\_iterator\_tag : public bidirectional\_iterator\_tag \{ \};