data structures using c++1 chapter 3 pointers dr. liu

Data Structures Using C++ 1

Chapter 3

Pointers

Dr. Liu


Chapter Objectives

• Learn about the pointer data type and pointer variables

• Explore how to declare and manipulate the pointer variables

• Learn about the address of operator and dereferencing operator

• Discover dynamic variables• Examine how to use the new and delete operators

to manipulate dynamic variables


Chapter Objectives

• Learn about pointer arithmetic• Discover dynamic arrays• Become aware of the shallow and deep

copies of data• Discover the peculiarities of classes with

pointer data members• Explore how dynamic arrays are used to

process lists


What are pointers ?

• Variables that store memory address

•How to De-reference pointers

•How to do Pointer assignment

•How to use address-of operator


What are pointers ?

5

3

8

1000

a

b

c

p

1000

1004

1008

1012

Address

int *p; int a = 5;p = &a; what is *p now ?;*p = *p + b; int c = *p;


Pointer Data Types and Pointer Variables

• Pointer variable: variable whose content is a memory address

• Syntax to declare pointer variable:dataType *identifier; e.g. int *p;

• Address of operator: Ampersand, &, e.g. &a

• Dereferencing operator: Asterisk, *


Pointers

• Statements:

int *p;

int num;


Pointers


Pointers

• Summary of preceding diagrams– &p, p, and *p all have different meanings– &p means the address of p– p means the content of p– *p means the content pointed to by p, that is

pointed to by the content of memory location


Pointers


Pointersx = 50;

p = &x;


Pointers

*p = 38;


Example 1

• // This program passes the address of a variable to a

• // function, which triples the value pointed to.

• Pointer example demo 1

• void triple_it(int *n);


Example 2

• // This program sorts an array from hightest member

• // down to lowest, in that order.

• Pointer example demo 2.

• void swap(int *p1, int *p2)


Example 3• void zero_out_array(int *arr, int n); void

zero_out_array(int *p, int n) {

• while (n-- > 0) { // Do n times:

• *p = 0; // Assign 0 to element // pointed to by p.

• p++; // Point to next element.

• }

• }


Classes, structs, and Pointer Variables

The syntax for accessing a class (struct) member using the operator -> is

pointerVariableName->classMemberName

Therefore, the statement

(*studentPtr).gpa = 3.9;

is equivalent to the statement

studentPtr->gpa = 3.9;


Syntax to use operator new

new dataType; //to allocate a single variable

new dataType[intExp]; //to allocate an array of variables


Syntax to use operator delete

delete pointer; //to destroy a single dynamic variable

delete [] pointer; //to destroy a dynamically created array


Operations on pointer variables

• Assignment operations

• Relational operations

• Limited arithmetic operations


Functions and Pointers

void example(int* &p, double *q)

{

.

.

.

}


Functions and Pointersvoid example(int* &p, double *q)

{

.

.

.

}


Pointers and Function Return Pointers

int* testExp(...)

{

.

.

.

}

is a pointer of the type int.


#include <stdio.h>

#define PRINTEM printf("%3d%5d%5d%5d%5d%5d\n", line++, num, x[0],x[1],x[2], ptr-x)

int main() {

static int x[] = {5,10,15}, lim =99;

int *ptr = x, num = 0;

int line = 0;

printf("LINE num x[0] x[1] x[2] ptr-x \n");

PRINTEM;

printf("\n\n");

num = *ptr; PRINTEM;

num = *++ptr; PRINTEM;

num = *ptr++; PRINTEM;

num = ++*ptr; PRINTEM;

num = (*ptr)++; PRINTEM;

num = ++(*ptr); PRINTEM;

num = *ptr + 1; PRINTEM;

num = *(ptr + 1); PRINTEM;

return 0;

}


Shallow Versus Deep Copy and Pointers



second = new int[10];

for(int j = 0; j < 10; j++)

second[j] = first[j];


Classes and Pointers: Some Peculiarities

class pointerDataClass

{

public:

...

private:

int x;

int lenP;

int *p;

};

pointerDataClass objectOne;

pointerDataClass objectTwo;


Classes and Pointers: Some Peculiarities


Destructor


Destructor

pointerDataClass::~pointerDataClass()

{

delete [ ] p;

}

class pointerDataClass{public: ~pointerDataClass();...private: int x; int lenP; int *p;};


Assignment Operator


Overloading the Assignment Operator

Function Prototype (to be included in the definition of the class):const className& operator=(const className&);

Function Definition:const className& className::operator=(const className&

rightObject){ //local declaration, if any if(this != &rightObject) //avoid self-assignment { //algorithm to copy rightObject into this object } //return the object assigned return *this;}


Overloading the Assignment Operator

• Definition of function operator=:– Only one formal parameter– Formal parameter generally const reference to

particular class– Return type of function is reference to

particular class


Copy Constructor


Copy Constructor

• If a class has pointer data members:– During object declaration, the initialization of one

object using the value of another object would lead to a shallow copying of the data if the default memberwise copying of data is allowed

– If, as a parameter, an object is passed by value and the default member-wise copying of data is allowed, it would lead to a shallow copying of the data


Copy Constructor

• The copy constructor automatically executes in the following situations– When an object is declared and initialized by

using the value of another object– When, as a parameter, an object is passed by

value– When the return value of a function is an object


Copy Constructor


Copy Constructor

General syntax to include the copy constructor in the definition of a class:

className(const className& otherObject);


Classes with Pointer Data Members

• Include destructor in the class

• Overload assignment operator for class

• Include copy constructor


Overloading Array Index (Subscript) Operator ([ ])

Syntax to declare the operator function operator [ ] as a member of a class for nonconstant arrays:

Type& operator[](int index);

Syntax to declare the operator function operator [ ] as a member of a class for constant arrays:

const Type& operator[](int index) const;


Chapter Summary

• Pointer data types and variables

• Dynamic variables

• Pointer arithmetic

• Dynamic arrays

• Shallow and deep copying

• Peculiarities of classes with pointer data members

data structures using c++1 chapter 3 pointers dr. liu

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