Ready knowledge
What is an iterator?
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Iterator is a bridge linking containers and algorithms, all algorithms are iterative data through the operation of the vessel
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Iterator is a smart pointer, the most important is the operator overloading
operator*,operator-> -
Implement iterators need to know the specific details of the container, so that each container corresponds to its own unique iterators, but the iterator interface is consistent
Traits programming skills
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Objective: extracting the data type stored in the container
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The core technology is the use of templates, you need to call to confirm the function at compile time
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Nested subordinate Name:
Template <typename T> class the Data { typedef the value_type T; }; Template <typename T> class the Type { // typename T :: the value_type is a nested slave name, which can not fall typename @ appreciated that template types using a template type the value_type the value_type typename T :: typedef; }; int main () { the type <the Data < int >> the value_type :: a (); // a () represents a variable of type int }
Placeholder parameters to achieve function overloading
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Placeholder parameter is a function parameter, but this parameter only parameter type, no parameters name
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Footprint parameter is also part of the list of parameters, can be achieved overloaded
// int parameter is a placeholder void Print ( int ) { COUT << " void Print (int) " << endl; } void Print () { COUT << " void Print () " << endl; } int main ( ) { Print ( . 1 ); // call Print void (int) Print (); // call Print void () }
Source
Common types corresponding iterator
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Commonly used in the iterator total 5 kinds of container type
Template < class the I> struct iterator_traits { typedef typename iterator_category iterator_category the I ::; typedef typename the value_type the value_type the I ::; typedef typename difference_type difference_type the I ::; typedef typename the I :: pointer pointer; typedef typename the I :: Reference Reference }; / * the value_type: iterator data type referred difference_type: indicates the type of the distance between two iterators of reference: the type of data content itself pointer: corresponding to the reference pointer type iterator_category: the Input the iterator: Read only Output iterator: write only Forward iterator: read and write, can only go forward, go forward every time a unit of bidirectional Iterator: read and write, two-way mobile, every time a mobile unit Random Access Iterator: readable and writable, two-way mobile, every time a plurality of mobile units * /
- Since the pointer type does not provide native types defined in 5, and therefore processing performed Laid
// Type achieve extraction of native pointer Template < class T> struct iterator_traits <T *> { ... typedef T * pointer; typedef T & Reference; }; // implementation type of the extracted pointer const, const attribute removed, as it will operation data container via the iterator Template < class T> struct iterator_traits < const T *> { ... typedef const T * pointer; typedef const T & Reference; };
- 5 kinds of type definition iterator_category, just type definition, no members
struct input_iterator_tag { }; struct output_iterator_tag { }; struct forward_iterator_tag : public input_iterator_tag { }; struct bidirectional_iterator_tag : public forward_iterator_tag { }; struct random_access_iterator_tag : public bidirectional_iterator_tag { };
iterator complete code
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Iterator type the relevant code
// five kinds iterator type struct input_iterator_tag {}; struct output_iterator_tag {}; struct forward_iterator_tag: public input_iterator_tag {}; struct bidirectional_iterator_tag: public forward_iterator_tag {}; struct random_access_iterator_tag: public bidirectional_iterator_tag {}; // define a base class that provides iteration type definition requires compiler to achieve succession, to prevent the omission Template < class the Category, class T, class Distance = ptrdiff_t, class the Pointer = T *, class Reference & = T> struct Iterator { typedef Category iterator_category; typedef T value_type; typedef Distance difference_type; typedef Pointer pointer; typedef Reference reference; }; // 类型提取 template <class Iterator> struct iterator_traits { typedef typename Iterator::iterator_category iterator_category; typedef typename Iterator::value_type typedef typename Iterator::difference_type typedef typename Iterator::pointer typedef typename Iterator::reference }; // 针对原生指针的特化处理 template <class T> struct iterator_traits<T*> { typedef random_access_iterator_tag iterator_category; typedef T value_type; typedef ptrdiff_t difference_type; typedef T* pointer; typedef T& reference; }; // 针对const指针的特化处理 template <class T> struct iterator_traits<const T*> { typedef random_access_iterator_tag iterator_category; typedef T value_type; typedef ptrdiff_t difference_type; typedef const T* pointer; typedef const T& reference; }; // 该函数非常方便的提取某个迭代器的类型iterator_category template <class Iterator> inline typename iterator_traits<Iterator>::iterator_category iterator_category(const Iterator&) { typedef typename iterator_traits<Iterator>::iterator_category category; return category(); } //This function is very convenient to extract a type of iterator difference_type Template < class the Iterator> inline typename iterator_traits <the Iterator> :: difference_type DISTANCE_TYPE * ( const the Iterator & ) { return static_cast <typename iterator_traits <the Iterator> :: difference_type *> ( 0 ) ; } // this function is very convenient to extract a type of iterator the value_type Template < class the iterator> inline typename iterator_traits <the iterator> :: * the value_type the value_type ( const the iterator & ) { return static_cast <typename iterator_traits <the iterator> :: * the value_type > ( 0 ); }
- advance function
// 迭代器前进 template <class InputIterator, class Distance> inline void advance(InputIterator& i, Distance n) { __advance(i, n, iterator_category(i)); } // radom迭代器前进 template <class RandomAccessIterator, class Distance> inline void __advance(RandomAccessIterator& i, Distance n, random_access_iterator_tag) { i += n; } // bidirectional迭代器前进 template <class BidirectionalIterator, class Distance> inline void __advance(BidirectionalIterator& i, Distance n, bidirectional_iterator_tag) { if (n >= 0) while (n--) ++i; else while (n++) --i; } // input迭代器前进 template <class InputIterator, class Distance> inline void __advance(InputIterator& i, Distance n, input_iterator_tag) { while (n--) ++i; }
- distance function
// 计算迭代器之间的距离 template <class InputIterator> inline iterator_traits<InputIterator>::difference_type distance(InputIterator first, InputIterator last) { typedef typename iterator_traits<InputIterator>::iterator_category category; return __distance(first, last, category()); } // 计算random迭代器之间的距离 template <class RandomAccessIterator> inline iterator_traits<RandomAccessIterator>::difference_type __distance(RandomAccessIterator first, RandomAccessIterator last, random_access_iterator_tag) { return last - first; } // 计算Input迭代器的距离 template <class InputIterator> inline iterator_traits<InputIterator>::difference_type __distance(InputIterator first, InputIterator last, input_iterator_tag) { iterator_traits<InputIterator>::difference_type n = 0; while (first != last) { ++first; ++n; } return n; }
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Not part of the standard STL, belonging to the SGI STL's proprietary code
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Iterator_traits same techniques and technologies, but the definition of different types, different occasions action
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The POD is a type defined __type_traits
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Part of the code as follows:
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struct __true_type { }; struct __false_type { }; template <class type> struct __type_traits { typedef __true_type this_dummy_member_must_be_first; typedef __false_type has_trivial_default_constructor; typedef __false_type has_trivial_copy_constructor; typedef __false_type has_trivial_assignment_operator; typedef __false_type has_trivial_destructor; typedef __false_type is_POD_type; // 是否是POD类型 }; __STL_TEMPLATE_NULL struct __type_traits<char> { typedef __true_type has_trivial_default_constructor; typedef __true_type has_trivial_copy_constructor; typedef __true_type has_trivial_assignment_operator; typedef __true_type has_trivial_destructor; typedef __true_type is_POD_type; }; __STL_TEMPLATE_NULL struct __type_traits<signed char> { typedef __true_type has_trivial_default_constructor; typedef __true_type has_trivial_copy_constructor; typedef __true_type has_trivial_assignment_operator; typedef __true_type has_trivial_destructor; typedef __true_type is_POD_type; }; __STL_TEMPLATE_NULL struct __type_traits<unsigned char> { typedef __true_type has_trivial_default_constructor; typedef __true_type has_trivial_copy_constructor; typedef __true_type has_trivial_assignment_operator; typedef __true_type has_trivial_destructor; typedef __true_type is_POD_type; }; __STL_TEMPLATE_NULL struct __type_traits<short> { typedef __true_type has_trivial_default_constructor; typedef __true_type has_trivial_copy_constructor; typedef __true_type has_trivial_assignment_operator; typedef __true_type has_trivial_destructor; __true_type is_POD_type typedef; }; // ... is defined for each base type // pointer native type defined Template < class T> struct __type_traits <T *> { typedef __true_type has_trivial_default_constructor; typedef __true_type has_trivial_copy_constructor; typedef __true_type has_trivial_assignment_operator ; typedef __true_type has_trivial_destructor; typedef __true_type is_POD_type; };