programming abstraction in c++qiao/courses/cs2so3/slides/linear.pdfprogramming abstraction in c++...

Introduction Stacks Queues Vectors

Programming Abstraction in C++

Eric S. Roberts and Julie Zelenski

Stanford University2010


Chapter 11. Linear Structures


Outline

1 Introduction

2 StacksArray implementationLinked list implementation

3 QueuesArray implementationLinked list implementation

4 Vectors


Introduction

Linear structures

Stack

Queue

Vector

Goals

Different (array and linked list) implementations of theselinear structures.

Introduce template in C++ and polymorphic classes.


Outline

1 Introduction



4 Vectors


Template

Changing CharStack to a general Stack template so the stackelement can be of any type.

Add the following line before a syntactic unit, such as classdefinition, and before each of the method implementations.

template <typename ElemType>


Example

Before class definition:

template <typename ElemType>class Stack {

public:

. . .

private:

#include "stackpriv.h"

};


Example

Before each of the method implementations:

template <typename ElemType>Stack<ElemType>::Stack {

capacity = INITIAL_CAPACITY;elements = new ElemType[capacity];count = 0;

}

Such classes are said to be polymorphic.


Interface

The interface Figure 11-1, pp. 384-385, remains the same asFigure 9-1, p. 320-321, except that the element type char isreplaced by ElemType.

Include different private data and implementation files to “hide”implementation detail.

private:#include "stackpriv.h"

#include "stackimpl.cpp"


Array implementation

Array implementation (partial):

Figure 11-2, Figure 11-3, pp. 386-387.

Almost identical to CharStack with dynamic array:

Figure 9-2, pp. 323-324, implementation on p. 326.


Linked list implementation

No cursor, no dummy cell.

The empty stack is represented by the NULL pointer.

count for the stack size.

The implementation of the methods is straightforward.Figures 11-4 and 11-5, pp. 388-390.


struct cellT {ElemType data;cellT *link;

};

cellT *list;int count;


stackimpl.cpp

template <typename ElemType>void Stack<ElemType>::push(ElemType elem) {

cellT *cell = new cellT;cell->data = elem;cell->link = list;list = cell;count++;

}


stackimpl.cpp

template <typename ElemType>ElemType Stack<ElemType>::pop() {

if (isEmpty()) {Error("pop: Empty stack");

}cellT *cell = list;ElemType result = cell->data;list = list->link;count--;delete cell;return result;

}


Outline

1 Introduction



4 Vectors


Interface

Interface, Figure 11-6, p. 392.

Similar to stack, except two operations

enqueue adds an element to the end of the queue

dequeue removes the first element from the queue



Two indexes: head and tail, for easy access to the firstand the end elements.




To use space efficiently, we “wrap around” the queue fromthe end of the array back to position 0.

tail

F G H I JK

5 1

0 1 2 3 4 5 6 7 8 9

head




To use space efficiently, we “wrap around” the queue fromthe end of the array back to position 0.

tail

F G H I JK

5 1

0 1 2 3 4 5 6 7 8 9

head

This representation is called ring buffer.


Array implementation (cont.)

Technique: modular arithmetic %Example. The size of the queue is

(tail + capacity - head) % capacity



Technique: modular arithmetic %Example. The size of the queue is

(tail + capacity - head) % capacity

When tail≥head, the size is tail−head= (tail +capacity - head) % capacity. When tail<head,unwrap the queue and the size is tail+capacity−head.



To avoid the confusion between an empty queue and a fullqueue, we limit the number of elements in the queue to oneless than the number of elements in the array. Thus thecondition for a full queue is

size() == capacity - 1

See the method enqueue, p. 307.



To avoid the confusion between an empty queue and a fullqueue, we limit the number of elements in the queue to oneless than the number of elements in the array. Thus thecondition for a full queue is

size() == capacity - 1

See the method enqueue, p. 307.

Private data, p. 319.

Implementation, Figure 11-7, pp. 396-398.



Two pointers: head and tail.

An empty queue is represented by NULL in head.

The enqueue must check for the empty queue as aspecial case.



Two pointers: head and tail.

An empty queue is represented by NULL in head.

The enqueue must check for the empty queue as aspecial case.

Similar to the linked list representation of the editor buffer.


enqueue

template <typename ElemType>void Queue<ElemType>::enqueue(ElemType elem) {

cellT *cellPtr = new cellT;cellPtr->data = elem;cellPtr->link = NULL;if (isEmpty()) {

head = cellPtr;} else {

tail->link = cellPtr;}tail = cellPtr;count++;

}


dequeue

template <typename ElemType>void Queue<ElemType>::isEmpty() {

return (head == NULL);}

template <typename ElemType>ElemType Queue<ElemType>::dequeue() {

if (isEmpty()) Error("...");

cellT *cellPtr = head;ElemType result = cellPtr->data;head = cellPtr->link;count--;delete cellPtr;return result;

}


Outline

1 Introduction



4 Vectors


Introduction

Dynamic array implementation. Similar to the dynamic arrayrepresentation of the editor buffer, for example, insertion anddeletion.


Introduction


New issues:

Check bounds.

Square bracket selection.

Iterator.


Introduction


New issues:

Check bounds.

Square bracket selection.

Iterator.

Interface, vector.h, Figure 11-11, pp. 405-408. It includesthe usual operations and square bracket operator and nestedclass Iterator.


vecpriv.h

Figure 11-12, p. 408

static const int INITIAL_CAPACITY = 100;

ElementType *elements;int capacity;int count;

void expandCapacity();

Similar to the array editor buffer, p. 347.


Check bounds

template <typename ElemType>void Vector<ElemType>::insertAt(int index, ElemType elem) {

if (count == capacity) expandCapacity();if (index < 0 || index > count) {

Error("insertAt: index out of range");}for (int i = count; i > index; i--) {

elements[i] = elements[i-1];}elements[index] = elem;count++;

}


Implementing selection brackets

Redefine operators for a particular class using the keywordoperator.

Return by reference using an &, so values can be assignedto an element selected using square brackets, for example,vec[i] = vec[i - 1].

template <typename ElemType>ElemType & Vector<ElemType>::operator[] (int index) {

if (index < 0 || index >= count) {Error("Vector selection index out of range");

}return elements[index];

}


Implementing iterators

A nested class, a class within a class. In vector.h:

Defining the Iterator class within the Vector class

class Iterator {public:

Iterator();bool hasNext();ElemType next();

private:Vector *vp;int index;

Iterator(Vector *vp);friend class Vector;

};friend class Iterator;


Implementing iterators (cont.)

The public section

public:Iterator();bool hasNext();ElemType next();

A public (Iterator) constructor, no parameters

Two public (Iterator) method prototypes



In the private section

private:Vector *vp;int index;

Iterator(Vector *vp);friend class Vector;

Two instance variables, as expected

A private constructor (with a parameter, a pointer toVector)

Designate Vector as a friend class, thus Vector classcan see the private variables, such as vp and index, andthe private constructor Iterator.



Outside the Iterator class, within the Vector class,

friend class Iterator;

Iterator iterator();

Designate Iterator as friend class, thus Iterator cansee private instance variables such as count.

Vector public method prototype iterator.



Idiom: Declaring an iteratorVector<int>::Iterator iter = vec.iterator();



Idiom: Declaring an iteratorVector<int>::Iterator iter = vec.iterator();

Implementation of Vector method iterator:

template <typename ElemType>typename Vector<ElemType>::Iterator

Vector<ElemType>::iterator() {return Iterator(this);

}

It calls Iterator private constructor passing this as theparameter and returns an object of Iterator class.Note. Vector can see Iterator private constructor.



Implementation of Iterator private constructor

template <typename ElemType>Vector<ElemType>::Iterator::Iterator(Vector *vp) {

this->vp = vp;index = 0;

}

It sets the Iterator instance variable vp to the parameterand index to 0.Note. Iterator now can see Vector private variablesthrough its own private variable vp.


Implementing vectors

Figure 11-12, p. 408, private data file.

Figure 11-13, pp. 409-412, implementation file.


Implementing vectors

Figure 11-12, p. 408, private data file.

Figure 11-13, pp. 409-412, implementation file.

Important. Changes to the content of a vector can invalidate theorder of elements returned by an iterator. For example, theVector method insertAt or removeAt can change thecontent of a vector, whereas Iterator has its own variableindex. In general, iterators make sense only if the structure isstatic.


A note on the typename keyword

The Vector method iterator on p. 411, the keywordtypename is required for a type/class that is defined inside aclass template when the reference is made outside of theimplementation of that class template.

Why is it outside? Because C++ considers the return type to beoutside the scope of the implementation. You are thereforerequired to qualify the name of the type by using the full nameVector<ElemType>::Iterator rather than just Iterator.You must also precede the return type with the keywordtypename because this type/class is defined within a template.

See p. 437, for the typename keyword.

programming abstraction in c++qiao/courses/cs2so3/slides/linear.pdfprogramming abstraction in c++...

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