List With Iterator (lab and HW)

完成伪标准：用伪迭代器列表完成mylist.h，一起写的声明和定义。

模板如下：

template<class T> 
class list { 
 public: 
  struct listelem;  // forward declarations 
  class iterator;
  list();
  list(size_t n_elements, const T& c);
  list(const list& x);
  list(iterator b, iterator e);
  ~list();
  iterator begin() const;
  iterator end() const;
  size_t size();
  void push_front(const T& c);
  void push_back(const T& c);
  void pop_front();
  void pop_back();
  iterator insert(iterator position, const T& val);
  iterator erase (iterator position);
  bool empty() const;
  T& front();
  T& back();
  void clear();
  friend ostream& operator << (ostream& out, const list& x);
  
  struct listelem {      // list cell 
    T data; 
    listelem *next, *prev; 
    listelem(const T& s, listelem* n, listelem* p);  // suggest u to use the constructor 
  };
  
  class iterator { 
   public: 
    friend class list;  // suggest u to use friend class
    explicit iterator(listelem* p = 0);

    iterator(const iterator& other) ;
    iterator& operator ++ ();
    iterator& operator -- ();
    iterator operator ++ (int);
    iterator operator -- (int);
    listelem* operator -> ();
    T& operator * ();
    
    // u can use iterator as listelem* sometimes
    operator listelem * () {return ptr;}  // conversion;
    
    private: 
    listelem* ptr;  // current listelem or 0; 
  };
  
  private: 
  iterator h, t;  // head and tail 
};

 

Sample input:

4

1 2 3 4

 

Sample output:

test size
0
empty
test push and pop
[ 1 ]
[ ]
[ 1 ]
[ ]
[ 1 ]
[ ]
[ 1 ]

8
[ 4 3 2 1 1 2 3 4 ]
[ 2 1 1 2 3 ]
front : 2
back : 3
not empty
test begin and end
2 1 1 2 3 
test insert and erase and ++ --
100
200
[ 100 2 1 1 2 3 200 ]
1
1
[ 100 1 2 3 200 ]
[ 99 101 100 1 2 3 200 ]
test constructor
[ 9 9 9 9 9 ]
[ 90 101 100 1 2 3 200 ]
[ 90 101 100 1 2 3 200 ]
[ 90 101 100 ]

mylist:

#include <iostream>#include <cassert>#include <string>using namespace std;  template<class T>class list { public:  struct listelem;  // forward declarations  class iterator;   list() {    h.ptr = t.ptr = 0;  }  // construct the empty list  list(size_t n_elements, const T& c) {    h.ptr = t.ptr = 0;    for ( size_t i = 0; i < n_elements; ++i )      push_front(c);  }   list(const list& x) {    list::iterator r = x.begin();    h.ptr = t.ptr = 0;    while (r != 0) {      push_back(*r++);    }  }   list(iterator b, iterator e)  {    h.ptr = t.ptr = 0;    while (b != e) {      push_back(*b++);    }  }   ~list() { clear(); }   iterator begin() const { return h; }   iterator end() const {    iterator temp = t;    return (temp.ptr == 0 ? iterator(0) : ++temp);  }   size_t size() {    size_t count = 0;    iterator temp = h;    while (temp != end()) {      temp++;      count++;    }    return count;  }   void push_front(const T& c) {    listelem* temp = new listelem(c, h, 0);    if (h.ptr != 0) {  // was a nonempty list      h->prev = temp;      h.ptr = temp;    } else {  // was an empty list      h.ptr = t.ptr = temp;    }  }   void push_back(const T& c) {    listelem* temp = new listelem(c, 0, t);    if (t != 0) {  // was a nonempty list      t->next = temp;      t.ptr = temp;    } else {  // was an empty list      h.ptr = t.ptr = temp;    }  }   void pop_front() {    listelem* temp = h.ptr;    if (h.ptr != 0) {      if (h.ptr == t.ptr) t.ptr = 0;      h.ptr = h->next;      if (h.ptr != 0) h->prev = 0;      delete temp;    }  }   void pop_back() {    listelem* temp = t.ptr;    if (t.ptr != 0) {      if (h.ptr == t.ptr) h.ptr = 0;      t.ptr = t->prev;      if (t.ptr != 0) t->next = 0;      delete temp;    }  }   iterator insert(iterator position, const T& val) {    listelem* p = position.ptr;    if (p == 0) {      // p == end()      push_back(val);      return t;    } else if (p->prev == 0) {      // p == begin()      push_front(val);      return begin();    } else {      listelem* temp = new listelem(val, p, p->prev);      p->prev = temp;      temp->prev->next = temp;      return iterator(temp);    }  }   iterator erase(iterator position) {    listelem* temp = position.ptr;    if (temp == h) {      // temp == begin();      pop_front();      return h;    }    temp->prev->next = temp->next;    temp->next->prev = temp->prev;    listelem* re = temp->next;    delete temp;    return iterator(re);  }   bool empty() const { return h.ptr == 0; }   T& front() { return *h; }  T& back() { return *t; }   void clear() {    while (h.ptr != 0) {      pop_front();    }    h.ptr = t.ptr = 0;  }   friend ostream& operator << (ostream& out, const list& x)  {    list<T>::iterator p = x.begin();    out << "[ ";    while (p != 0) {      out << *p << " ";      ++p;  // advances iterator using next    }    out << "]";    return out;  }   struct listelem {      // list cell    T data;    listelem *next, *prev;    listelem(const T& s, listelem* n, listelem* p) \      : data(s), next(n), prev(p) {}  };  // scopeed within class list   class iterator {   public:    friend class list;    explicit iterator(listelem* p) : ptr(p) {}    iterator() : ptr(0) {}    iterator& operator++() {      ptr = ptr->next;      return *this;    }     iterator& operator--() {      ptr = ptr->prev;      return *this;    }     iterator operator++(int) {      iterator temp = *this;      ptr = ptr->next;      return temp;    }     iterator operator--(int) {      iterator temp = *this;      ptr = ptr->prev;      return temp;    }     listelem* operator -> () { return ptr; }    T& operator * () { return ptr->data; }    operator listelem * () { return ptr; }  // conversion    private:    listelem* ptr;  // current listelem or 0;  };  private:  iterator h, t;  // head and tail};