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  1. #include <iostream>
  2.  
  3. using namespace std;
  4.  
  5. // 12. Complete the definition of list from §20.4.1–2 and get the high() example to run.
  6. // Allocate a Link to represent one past the end.
  7.  
  8. template<typename Elem>
  9. struct Link
  10. {
  11.           Link* prev;               // previous link
  12.           Link* succ;               // successor (next) link
  13.           Elem val;                   // the value
  14. };
  15.  
  16. template<typename Elem>
  17. class list {
  18.           // representation and implementation details
  19.           Link<Elem>* first;
  20.           Link<Elem>* last;    // one beyond the last link
  21. public:
  22.           list() { Link<Elem>* node = new Link<Elem>; first = node; last = node; }
  23.  
  24.           class iterator;                 // member type: iterator
  25.  
  26.           iterator begin();            // iterator to first element
  27.           iterator end();              // iterator to one beyond last element
  28.  
  29.           iterator insert(iterator p, const Elem& v);        // insert v into list after p
  30.           iterator erase(iterator p);                                    // remove p from the list
  31.  
  32.           void push_back(const Elem& v);                      // insert v at end
  33.           void push_front(const Elem& v);                     // insert v at front
  34.           void pop_front();          // remove the first element
  35.           void pop_back();          // remove the last element
  36.  
  37.           Elem& front();               // the first element
  38.           Elem& back();               // the last element
  39.  
  40.           // . . .
  41. };
  42.  
  43. //--------------------------------------------------------------------------------------------
  44.  
  45. // this push_front() function isn't working as it is supposed to; there's no link from first and last to it
  46. template <typename Elem>
  47. void list<Elem>::push_front(const Elem& v)
  48. {
  49.     Link<Elem>* newNode = new Link<Elem>;
  50.     newNode->val = v;
  51.     newNode->prev = nullptr;
  52.     newNode->succ = first;
  53.     first = newNode;
  54. }
  55.  
  56. template <typename Elem>
  57. typename list<Elem>::iterator list<Elem>::begin()
  58. {
  59.     return first;
  60. }
  61.  
  62. template <typename Elem>
  63. typename list<Elem>::iterator list<Elem>::end()
  64. {
  65.     return last;
  66. }
  67.  
  68.  
  69. //---------------------------------Exercise 19--------------------------------------------
  70.  
  71. template<typename Elem>         // requires Element<Elem>() (§19.3.3)
  72. class list<Elem>::iterator {
  73.           Link<Elem>* curr;              // current link
  74. public:
  75.           iterator(Link<Elem>* p) :curr{p} { }
  76.  
  77.           iterator& operator++()
  78.           {
  79.               if (curr->succ == nullptr)
  80.               {
  81.                   // error("Can't increment; pointer out of scope.");
  82.                   cout << "Can't increment; pointer out of scope." << endl;
  83.               }
  84.               curr = curr->succ;
  85.               return *this;
  86.  
  87.           }   // forward
  88.           iterator& operator--()
  89.           {
  90.               if (curr->prev == nullptr)
  91.               {
  92.                   // error("Can't decrement; pointer out of scope.");
  93.                   cout << "Can't increment; pointer out of scope." << endl;
  94.               }
  95.               curr = curr->prev;
  96.               return *this;
  97.           }   // backward
  98.           Elem& operator*() { return curr->val; }   // get value (dereference)
  99.  
  100.           bool operator==(const iterator& b) const { return curr==b.curr; }
  101.           bool operator!= (const iterator& b) const { return curr!=b.curr; }
  102. };
  103.  
  104. //---------------------------------Exercise 19--------------------------------------------
  105.  
  106. int main()
  107. {
  108.     list<int> l;
  109.     l.push_front(2);
  110.     l.push_front(3);
  111.     l.push_front(4);
  112.     l.push_front(5);
  113.     list<int>::iterator it = l.begin();
  114.     for (; it != l.end(); ++it)
  115.     {
  116.         cout << *it << endl;
  117.     }
  118.     cout << "-------------------------------------------" << endl;
  119.     ++it;
  120.     cout << *it << endl;
  121.     ++it;
  122.     cout << *it << endl;
  123.     ++it;
  124.     cout << *it << endl;
  125.     ++it;
  126.     cout << *it << endl;
  127.     ++it;
  128.     cout << *it << endl;
  129.     return 0;
  130. }
  131.  
Runtime error #stdin #stdout 0s 16064KB
comments (?)
stdin 
Standard input is empty
stdout 
5
4
3
2
-------------------------------------------
Can't increment; pointer out of scope.
https://ideone.com/tVQYey
language:
C++ (gcc 8.3)
created:
8 years ago
visibility:
public

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