迭代器概念與Traits程式設計技法
阿新 • • 發佈：2019-01-05
1 #include <iostream> 2 using namespace std; 3 4 template <class T> 5 struct MyIter 6 { 7 typedef T value_type; 8 T* ptr; 9 MyIter(T *p = 0) : ptr(p) {} 10 T& operator*() const { return *ptr; } 11 }; 12 13 template <class I> 14 typename I::value_type func(I ite)15 { 16 return *ite; 17 } 18 19 int main() 20 { 21 MyIter<int> iter1(new int(8)); 22 cout << func(iter1) << " "; 23 MyIter<char> iter2(new char('a')); 24 cout << func(iter2) << " "; 25 system("pause"); 26 return 0; 27 }
輸出結果：
1 /* https://blog.csdn.net/damotiansheng/article/details/41379151 */ 2 3 #include <iostream> 4 #include <new.h> 5 //using namespace std; //不要std,因為std名稱空間中也有input_iterator_tag等的定義 6 7 struct input_iterator_tag {}; //std名稱空間中也有input_iterator_tag的定義 8 struct output_iterator_tag {};9 struct forward_iterator_tag: public input_iterator_tag {}; 10 struct bidirectional_iterator_tag: public forward_iterator_tag {}; 11 struct random_access_iterator_tag: public bidirectional_iterator_tag {}; 12 13 struct __true_type {}; 14 struct __false_type {}; 15 16 template <class T1, class T2> 17 inline void construct( T1 *p, const T2& value ) 18 { 19 new (p) T1(value); 20 return; 21 } 22 23 24 template <class OutputIterator, class Size, class T> 25 OutputIterator fill_n( OutputIterator first, Size n, const T& value) 26 { 27 for( ; n > 0; --n, ++first) 28 { 29 *first = value; 30 } 31 return first; 32 } 33 34 template <class Category, class T, class Distance = ptrdiff_t, class Pointer = T*, class Reference = T&> 35 struct iterator 36 { 37 typedef Category iterator_category; 38 typedef T value_type; 39 typedef Distance difference_type; 40 typedef Pointer pointer; 41 typedef Reference reference; 42 }; 43 44 template <class Iterator> 45 struct iterator_traits // iterator_traits負責萃取迭代器的特性，例如獲得迭代器指向元素的型別等 46 { 47 typedef typename Iterator::iterator_category iterator_category; 48 typedef typename Iterator::value_type value_type; 49 typedef typename Iterator::difference_type difference_type; 50 typedef typename Iterator::pointer pointer; 51 typedef typename Iterator::reference reference; 52 }; 53 54 template <class T> 55 struct iterator_traits<T*> 56 { 57 typedef random_access_iterator_tag iterator_category; 58 typedef T value_type; 59 typedef ptrdiff_t difference_type; 60 typedef T* pointer; 61 typedef T& reference; 62 }; 63 64 template <class Iterator> 65 inline typename iterator_traits<Iterator>::value_type* value_type( const Iterator&) 66 { 67 return static_cast<typename iterator_traits<Iterator>::value_type*>(0); 68 } 69 70 template <class type> 71 struct __type_traits 72 { 73 typedef __false_type has_trivial_default_constructor; 74 typedef __false_type has_trivial_copy_constructor; 75 typedef __false_type has_trivial_assignment_operator; 76 typedef __false_type has_trivial_destructor; 77 typedef __false_type is_POD_type; 78 }; 79 80 template <> 81 struct __type_traits<int> 82 { 83 typedef __true_type has_trivial_default_constructor; 84 typedef __true_type has_trivial_copy_constructor; 85 typedef __true_type has_trivial_assignment_operator; 86 typedef __true_type has_trivial_destructor; 87 typedef __true_type is_POD_type; 88 }; 89 90 template <class ForwardIterator, class Size, class T> 91 inline ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n, const T& x) 92 { 93 return __uninitialized_fill_n( first, n, x, value_type(first)); 94 } 95 96 template <class ForwardIterator, class Size, class T, class T1> 97 inline ForwardIterator __uninitialized_fill_n( ForwardIterator first, Size n, const T& x, T1* ) 98 { 99 typedef typename __type_traits<T1>::is_POD_type is_POD; 100 return __uninitialized_fill_n_aux( first, n, x, is_POD()); 101 } 102 103 template <class ForwardIterator, class Size, class T> 104 inline ForwardIterator __uninitialized_fill_n_aux( ForwardIterator first, Size n, const T& x, __true_type ) 105 { 106 return fill_n( first, n, x); 107 } 108 109 template <class ForwardIterator, class Size, class T> 110 ForwardIterator __uninitialized_fill_n_aux( ForwardIterator first, Size n, const T& x, __false_type) 111 { 112 ForwardIterator cur = first; 113 for( ; n > 0; --n, ++cur ) 114 { 115 construct( &*cur, x); 116 } 117 return cur; 118 } 119 120 class Test 121 { 122 public: 123 Test(int n = 0) 124 { 125 std::cout << "Test::Test(" << n << ")被呼叫\n"; 126 data = n; 127 } 128 int operator()() { return data; } 129 int operator int() { return data; } 130 private: 131 int data; 132 }; 133 134 int main() 135 { 136 int a[] = { 1, 2, 3, 4, 5 }; 137 int *begin = &a[0]; 138 uninitialized_fill_n(begin, 5, 1); 139 140 for( int i = 0; i < 5; i++ ) 141 std::cout << a[i] << ' '; //輸出5個1 142 143 std::cout << std::endl; 144 Test array[5]; //呼叫5次建構函式 145 Test *pT = &array[0]; 146 uninitialized_fill_n( pT, 5, 2); //呼叫5次建構函式 147 148 for( int i = 0; i < 5; i++ ) 149 std::cout << array[i] << ' '; //輸出5個2 150 151 std::cout << std::endl; 152 system("pause"); 153 return 0; 154 }
1 /* https://blog.csdn.net/damotiansheng/article/details/41379151 */ 2 3 #include <iostream> 4 #include <new.h> 5 //using namespace std; //不要std,因為std名稱空間中也有input_iterator_tag等的定義 6 7 struct input_iterator_tag {}; //std名稱空間中也有input_iterator_tag的定義 8 struct output_iterator_tag {}; 9 struct forward_iterator_tag: public input_iterator_tag {}; 10 struct bidirectional_iterator_tag: public forward_iterator_tag {}; 11 struct random_access_iterator_tag: public bidirectional_iterator_tag {}; 12 13 struct __true_type {}; 14 struct __false_type {}; 15 16 template <class T1, class T2> 17 inline void construct( T1 *p, const T2& value ) 18 { 19 new (p) T1(value); 20 return; 21 } 22 23 24 template <class OutputIterator, class Size, class T> 25 OutputIterator fill_n( OutputIterator first, Size n, const T& value) 26 { 27 for( ; n > 0; --n, ++first) 28 { 29 *first = value; 30 } 31 return first; 32 } 33 34 template <class Category, class T, class Distance = ptrdiff_t, class Pointer = T*, class Reference = T&> 35 struct iterator 36 { 37 typedef Category iterator_category; 38 typedef T value_type; 39 typedef Distance difference_type; 40 typedef Pointer pointer; 41 typedef Reference reference; 42 }; 43 44 template <class Iterator> 45 struct iterator_traits // iterator_traits負責萃取迭代器的特性，例如獲得迭代器指向元素的型別等 46 { 47 typedef typename Iterator::iterator_category iterator_category; 48 typedef typename Iterator::value_type value_type; 49 typedef typename Iterator::difference_type difference_type; 50 typedef typename Iterator::pointer pointer; 51 typedef typename Iterator::reference reference; 52 }; 53 54 template <class T> 55 struct iterator_traits<T*> 56 { 57 typedef random_access_iterator_tag iterator_category; 58 typedef T value_type; 59 typedef ptrdiff_t difference_type; 60 typedef T* pointer; 61 typedef T& reference; 62 }; 63 64 template <class Iterator> 65 inline typename iterator_traits<Iterator>::value_type* value_type( const Iterator&) 66 { 67 return static_cast<typename iterator_traits<Iterator>::value_type*>(0); 68 } 69 70 template <class type> 71 struct __type_traits 72 { 73 typedef __false_type has_trivial_default_constructor; 74 typedef __false_type has_trivial_copy_constructor; 75 typedef __false_type has_trivial_assignment_operator; 76 typedef __false_type has_trivial_destructor; 77 typedef __false_type is_POD_type; 78 }; 79 80 template <> 81 struct __type_traits<int> 82 { 83 typedef __true_type has_trivial_default_constructor; 84 typedef __true_type has_trivial_copy_constructor; 85 typedef __true_type has_trivial_assignment_operator; 86 typedef __true_type has_trivial_destructor; 87 typedef __true_type is_POD_type; 88 }; 89 90 template <class ForwardIterator, class Size, class T> 91 inline ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n, const T& x) 92 { 93 return __uninitialized_fill_n( first, n, x, value_type(first)); 94 } 95 96 template <class ForwardIterator, class Size, class T, class T1> 97 inline ForwardIterator __uninitialized_fill_n( ForwardIterator first, Size n, const T& x, T1* ) 98 { 99 typedef typename __type_traits<T1>::is_POD_type is_POD; 100 return __uninitialized_fill_n_aux( first, n, x, is_POD()); 101 } 102 103 template <class ForwardIterator, class Size, class T> 104 inline ForwardIterator __uninitialized_fill_n_aux( ForwardIterator first, Size n, const T& x, __true_type ) 105 { 106 return fill_n( first, n, x); 107 } 108 109 template <class ForwardIterator, class Size, class T> 110 ForwardIterator __uninitialized_fill_n_aux( ForwardIterator first, Size n, const T& x, __false_type) 111 { 112 ForwardIterator cur = first; 113 for( ; n > 0; --n, ++cur ) 114 { 115 construct( &*cur, x); 116 } 117 return cur; 118 } 119 120 class Test 121 { 122 public: 123 Test(int n = 0) 124 { 125 std::cout << "Test::Test(" << n << ")被呼叫\n"; 126 data = n; 127 } 128 int operator()() { return data; } 129 int operator int() { return data; } 130 private: 131 int data; 132 }; 133 134 int main() 135 { 136 int a[] = { 1, 2, 3, 4, 5 }; 137 int *begin = &a[0]; 138 uninitialized_fill_n(begin, 5, 1); 139 140 for( int i = 0; i < 5; i++ ) 141 std::cout << a[i] << ' '; //輸出5個1 142 143 std::cout << std::endl; 144 Test array[5]; //呼叫5次建構函式 145 Test *pT = &array[0]; 146 uninitialized_fill_n( pT, 5, 2); //呼叫5次建構函式 147 148 for( int i = 0; i < 5; i++ ) 149 std::cout << array[i] << ' '; //輸出5個2 150 151 std::cout << std::endl; 152 system("pause"); 153 return 0; 154 }View Code