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technoXavage 04.10.2001 01:43

queue linked implementation
template <class T><BR>class Queue<BR>{<BR> public:<BR> Queue();<BR> Queue(const Queue&);<BR> ~Queue();<BR> Queue& operator=(const Queue&);<BR> int size() const;<BR> bool empty() const;<BR> T& front();<BR> T& back();<BR> void push(const T&);<BR> void pop();<BR> void dispValues();<BR> protected:<BR> class Node<BR> {<BR> public:<BR> Node(const T& x, Node* next=0) : _(x), _next(next) {}<BR> T _;<BR> Node* _next;<BR> };<BR> Node *_front, _back;<BR> int _size;<BR>};

template <class T> Queue<T>::Queue() : _back(0), _size(0)<BR>{<BR>}

template <class T><BR>Queue<T>::Queue(const Queue& s) : _back(0), _size(s._size)<BR>{<BR> if (_size==0) return;<BR> Node* pp=0;<BR> for (Node* p = s._back; p; p = p->_next)<BR> if (p==s._back) pp = _back = new Node(p->_);<BR> else pp = pp->_next = new Node(p->_);<BR>}

template <class T> Queue<T>::~Queue()<BR>{<BR> while (_back) <BR> {<BR> Node* p=_back;<BR> _back = _back->_next;<BR> delete p;<BR> }<BR>}

template <class T> int Queue<T>::size() const<BR>{<BR> return _size;<BR>}

template <class T> bool Queue<T>::empty() const<BR>{<BR> return _size==0;<BR>}

template <class T> T& Queue<T>::front()<BR>{<BR> return _front->_;<BR>}

template <class T> T& Queue<T>::back()<BR>{<BR> return _back->_;<BR>}

template <class T> void Queue<T>: <IMG SRC="tongue.gif" border="0">ush(const T& x)<BR>{<BR> if (_size==0) _front = _back = new Node(x);<BR> else _back = _back->_next = new Node(x);<BR> ++_size;<BR>}

template <class T> void Queue<T>: <IMG SRC="tongue.gif" border="0">op()<BR>{<BR> Node* p = _front;<BR> _front = _front->_next;<BR> delete p;<BR> --_size;<BR>}

<BR>template <class T><BR>void Queue<T>:: dispValues()<BR>{<BR> cout << "front = " << _front << endl;<BR> cout << "back = " << _back << endl;<BR> cout << "size = " << _size << endl;<BR> for ( Node* p = _front; p; p = p->_next)<BR> cout << p->_ << endl;<BR>}

template <class T><BR>void print(const Queue<T> &ss)<BR>{<BR> Queue<T> s = ss;<BR> cout << "size = " << s.size();<BR> if (s.size() > 0)<BR> {<BR> cout << ", back=" << s.back() << ": (" << s.front();<BR> s.pop();

while (!s.empty())<BR> {<BR> cout << "," << s.front();<BR> s.pop();<BR> }<BR> cout << ")";

}<BR> cout << endl;<BR>}

void main()<BR>{<BR> Queue<string> s; print(s);<BR> s.push("first"); print(s);<BR> s.push("second"); print(s);<BR> s.push("third"); print(s);<BR> s.pop(); print(s);<BR> s.push("fourth"); print(s);<BR> s.push("fifth"); print(s);<BR> s.push("sixth"); print(s);<BR> s.pop(); print(s);<BR>// s.dispValues();<BR>}

<BR>//need help with debuggin

Alexandr 14.10.2001 15:16

First of all there are some things in your code that you should be careful of. The first one is the return value of these functions:<BR>T& front() and T& back()<BR>The reference is the same thing as the object and that means it can be used as an L-value. So using this functions is the same as using your private variables in the left side of operator=. To avoid this problem you can either return just the value, or change the functions to this type:<BR>const T& front() and const T& back().<BR>This will help you to avoid more problems.

<BR>The second thing I saw was the often use of '_' symbol. That is not forbidden of course but may cause nasty problems.

"Names starting with underline symbol are reserved for specific demands of realization and running envoirment, thats why they should not be used in your applications."

-B. Stroustrup "C++ programming language" p.120

<BR>Well what about your debugging problems. When I copied your program and launched the debug process the compiler found several errors, but the program was so unreadable that I just did not try to have a look. Please, choose a more cute style of writing your application codes.

Good luck.

[ October 14, 2001: Message edited by: Alexandr ]

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