chapter 5: pointers and strings

Chapter 5: Pointers and Strings

OutlineIntroduction

Pointer Variable Declarations and Initialization Pointer Operators

Pointer of Complex StructureOther Pointer OperationsCalling Functions by ReferenceRelationship between pointer and arrayDynamic Data Storage

Introduction

• Pointers – Powerful, but difficult to master– Simulate pass-by-reference – Close relationship with arrays and strings

Pointer Variable Declarations and Initialization

• Pointer variables– Contain memory addresses as values – Normally, variable contains specific value (direct reference)– Pointers contain address of variable that has specific value

(indirect reference)• Indirection

– Referencing value through pointer• Pointer declarations

– * indicates variable is pointerint *countPtr;

declares pointer to int, pointer of type int *– Multiple pointers require multiple asterisks

int *myPtr1, *myPtr2;

countPtr

Pointer Variable Declarations and Initialization

• Can declare pointers to any data type• Pointer initialization

– Initialized to 0, NULL, or address• 0 or NULL points to nothing

Pointer Operators

• & (address operator)– Returns memory address of its operand– Example

int y = 5;int *yPtr;yPtr = &y; // yPtr gets address of y

– yPtr “points to” y

600004 600000

600000 5

address of y is value of yptr

Pointer Operators

• * (indirection/dereferencing operator)– Returns synonym for object its pointer operand points to– *yPtr returns y (because yPtr points to y).– dereferenced pointer is lvalue

*yptr = 9; // assigns 9 to y• * and & are inverses of each other• Example 1 #include <iostream>

int main()

{ int *p;

int q=3, k=5;

cout << "p is " <<p<<" *p is " <<*p<<" q is "<<q<<endl;

return 0;

Pointer Operators

Pointer of complex structure

• Example 2#include <iostream>

struct Student{

int grade;

char name[20];

int main()

struct Student *p, q;

q.grade = 90;

strcpy(q.name,"Smith");

cout << "Grade " <<q.grade<< " Name " <<q.name<<endl;

cout << "Grade " << p->grade <<" Name "<<p->name<<endl;

return 0;

Pointer of complex structure

Other Pointer Operations

• Example 3

#include <iostream>

int main()

int i=3, j=3, *p1, *p2;

p1=&i, p2=&j;

if(*p1==*p2) //used to check if the content is the same.

cout <<"*p1 Equal to *p2"<<endl;

else cout<<"*p1 not Equal to *p2"<<endl;

if(p1==p2) //used to check if they are pointing to the same unit.

cout <<"p1 Equal to p2"<<endl;

else cout <<"p1 not Equal to p2"<<endl;

if(p1<=p2) //it has side-effect, do not use it.

cout <<"p1 no more than p2"<<endl;

else cout <<"p1 less than p2"<<endl;

return 0;

Other Pointer Operations

Calling Functions by Reference

• 3 ways to pass arguments to function– Pass-by-value arguments– Pass-by-reference with reference arguments– Pass-by-pointer arguments

• return can return one value from function• Example 4

Calling Functions by Reference#include <iostream>

void f_point( int *i, int *j)

void f_reference( int &i, int &j)

void f_value (int i, int j)

int main()

int p=1, q=2;

f_point(&p,&q);

cout << "p is "<< p << " q is " <<q <<endl;

f_reference(p,q);

f_value(p,q);

return 0;

Calling Functions by Reference

Relationship Between Pointers and Arrays

• Arrays and pointers closely related– Array name like constant pointer– Pointers can do array subscripting operations

• Pointer variable and name of array

Name of array (Note that all elements of this array starts from here, c)

Position number of the element within array c

Pointer pointing to the address of c[0]

Name of array (Note that all elements of this array starts from here, c)

Last element

*(pointer+0), or *p

*(pointer+7)

• Accessing array elements with pointers– Element b[ n ] can be accessed by *( bPtr + n )

• Called pointer/offset notation– Addresses

• &b[ 3 ] same as bPtr + 3– Array name can be treated as pointer

• b[ 3 ] same as *( b + 3 )– Pointers can be subscripted (pointer/subscript notation)

• bPtr[ 3 ] same as b[ 3 ]

#include <iostream>

void f_point( char * i, char * j)

*(i+2)='E';

*(j+3)='E';

void f_array( char i[], char j[])

i[2]='E';

j[3]='E';

int main()

char p[6]="hello", q[10]="howareyou";

f_point(p,q);

strcpy(p,"hello");

strcpy(q,"howareyou");

f_array(p,q);

return 0;

•Example 5

Dynamic Data Storage

• Dynamic memory management– Control allocation and deallocation of memory– Operators new and delete

• new operator– Create memory for object– Calls default constructor for object– Returns pointer of specified type– Format

• Providing initializersdouble *ptr = new double( 3.14159 );Time *timePtr = new time( 12, 0, 0 );• Allocating arraysint *gradesArray = new int[ 10 ];

• Example 6

• delete– Destroy dynamically allocated object and free space– Operator delete

• Calls destructor for object• Deallocates memory associated with object

– Memory can be reused to allocate other objects– Deallocating arrays

• delete [] gradesArray;– First calls destructor for each object in array– Then deallocates memory

• delete time;

• Example 6 #include <iostream>

#include <string>

int main()

char * p;

int index;

cout << "Input how many characters:" ;

cin >>index;

p = new char [index+1];

cin >> p;

cout <<"p is: " <<p;

delete [] p;

p=NULL;

return 0;

• Example 7: Multiple-phase development– Step 1: 7_1.cc– Step 2: 7_2.cc– Step 3: 7_3.cc

• 7_3.cc#include <iostream>

class MyArray{

public:

MyArray();

MyArray(int);

~MyArray();

void printall();

void array_copy(MyArray&);

private:

int size;

int *ptr;

MyArray::MyArray()

size=0;

ptr=NULL;

MyArray::MyArray(int t_size)

if(t_size>0){

size=t_size;

ptr=new int[t_size+1];

cout << "Please input "<<t_size<< " intergers:";

for(int i=0;i<t_size;i++)

cin >> ptr[i];

size=0;

ptr=NULL;

MyArray::~MyArray()

size=0;

delete [] ptr;

Dynamic Data Storage• 7_3.cc (continue)void MyArray::printall()

if(size==0) {

cout <<"NULL"<<endl;

return;

for(int i=0;i<size;i++)

cout<<ptr[i]<<" ";

cout <<endl;

void MyArray::array_copy(MyArray & b)

size=b.size;

delete [] ptr;

ptr=new int [size+1];

for(int i=0; i<size;i++)

ptr[i]=b.ptr[i];

ptr[size]=0;

int main()

MyArray a, b(4);

cout << "Before copying"<<endl;

a.printall();

b.printall();

a.array_copy(b);

cout << "After copying"<<endl;

a.printall();

b.printall();

return 0;

chapter 5: pointers and strings

Documents

strings, arrays, and pointers cs-2303, c-term 20101 strings,...

chapter 5 - pointers and strings

1 pointers and strings chapter 5 2 what you will learn... ...

pointers and strings section 5.4, 5.7-5.10, 5.12.1

strings, arrays, and pointers

chapter 5 array, pointers and strings

pointer in c++ dr. ahmed telba. topics covered introduction...

programmeren in c: 3. arrays, pointers en strings

pointers and strings

c arrays, strings, more pointers

c: pointers, arrays, and strings -...

1 chapter 6 arrays, pointers, and strings 2008-11-25

structures, headers, arrays, functions, strings, pointers in...

arrays, strings, and pointers - cvut.cz...arrays, strings,...

bcanew - university of calicutprograms involving pointers,...

programming review: functions, pointers and strings

strings, arrays (and pointers) strings, arrays (and...

5. arrays, pointers and strings - iit kanpur

chapter 6 arrays, pointers, and strings 6.1 one...

coen 244 - 8 - pointers and pointer-based strings