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1 Main IndexMain Index ContentsContents1 Main IndexMain Index ContentsContents

Pointer Illustration

Vertical / Horizontal View . . .

Data Addresses in Memory

Declaring Pointer Variables

Assigning Values to Pointers

Accessing Data with Pointers

Arrays and Pointers

Operator ‘new’

Operator ‘delete’

Illustrating the Destructor

Copy Constructor / Overloaded Assignment Operator

Declaration of dynamicClass Objects

Chapter 5 Chapter 5 – – Pointers and Dynamic MemoryPointers and Dynamic Memory

The Pointer ‘this’dynamicClass Copy ConstructorThe C++ Index Operator []MatricesSummary Slides (3 pages)


Pointer IllustrationPointer Illustration

A d d res s

D at a co n t en t s


Vertical and Horizontal View of Vertical and Horizontal View of MemoryMemory

A d d res s 0

A d d res s n

A d d res s 2

A d d res s 1

A d d r 0 A d d r 1 A d d r 2 Ad d r n

Vert ical V iew o f M em o ry

H o riz o n t al V iew o f M em o ry

...

. . .


Data Addresses in MemoryData Addresses in Memory

50

in t eger ch ar

5 0 0 0

S

5 0 0 4 5 0 0 5


Declare a pointer by stating the type followed by the variable name, but with a "*" added immediately before the name.

The pointer ptr is a variable whose value is the address of a data item of the designated type.

Declaring Pointer VariablesDeclaring Pointer Variables

int *intPtr;

char *charPtr;

type *ptr;

6 Main IndexMain Index ContentsContents

Assigning Values to PointersAssigning Values to Pointers

&m is the address of the integer in memory. The assignment statement

sets intPtr to point at an actual data item.

The Figure illustrates the status of the two variables from the declaration statement and the resulting status after the assignment of a value to intPtr.

intPtr = &m;

int m = 50, *intPtr;

5 0m

?in tP tr

?

5 0

m

& m

in tP tr(a) A fte r d e c laratio n (b ) A fte r as s ig n m e n t


Accessing Data with PointersAccessing Data with Pointers

int x = 50, y = 100,

*px = &x, *py = &y;

5 0

x

p x

1 0 0

y

p y


Arrays and PointersArrays and Pointers

a rr

a rr[0 ] a rr[6 ]a rr[5 ]a rr[4 ]a rr[3 ]a rr[2 ]a rr[1 ]

a rr+ 7a rr+ 2a rr+ 1

6000 602860206016601260086004 6032

a rr+ 5


Operator ‘new’Operator ‘new’p = new time24;// *p is 00:00 (midnight)q = new time24(8, 15);// *q is 8:15 AM

H e a p

p .h o u r

q .m in u te

q .h o u r

p .m in u te

00

15

08

00

p

q


Operator ‘delete’Operator ‘delete’

deallocating a dynamic array, use a slightly different form of delete. Place square brackets [] between delete and the pointer variable name. The system deallocates all of the memory originally assigned to the dynamic array.

arr = new T[ARRSIZE];

// allocated space for ARRSIZE objects

delete [] arr;

// deallocate dynamic array storage


Illustrating the DestructorIllustrating the Destructor

m e m be r1= m 1

B e fo re de s tro ying o bj Af te r de s tro ying o bj

m e m be r2m e m be r1= m 1 m e m be r2

m 2 m 2

O n he ap

\\

R e m ains o n the he ap with no thingpo int ing at i t .


Copy Constructor / Overloaded Copy Constructor / Overloaded Assignment OperatorAssignment Operator

15

30

y

(a ) In i ti a l i z a ti on : ti m e 24 y = x

15

30

x

0

0

y

(b) As s i gn m e n t: z = x

15

30

x

15

30

Initialization and Assignment

both have the effect of producing a data item

that is a copy of an existing item


Declaration of dynamicClass Declaration of dynamicClass ObjectsObjects

o b jA

m em b er1 = 1 m em b er2

* o b jA .m em b er2 = 2

H eap m em o ry

• The byte-by-byte copy performed by default by C++ is inappropriate for dynamic classes• The copy of an objA in ObjB makes two pointers point at the same memory location.

•This creates a memory leak when one of the two objects is deleted.


The Pointer ‘this’The Pointer ‘this’

*this objA;

this-> memberl


dynamicClass Copy Constructor dynamicClass Copy Constructor AlgorithmAlgorithm

m e m b e r1 = 3

o b jB

m e m be r 2m e m be r1 = 3 m e m be r 2

* o bjB .m e m be r2 = 5

o b jA

* o b jA .m e m b e r2 = 5

# 1 : c o py c o nte nts

# 2 : allo c ate * m e m b e r2

# 3 : c o py c o nte nts

Example:dynamicClass<int> obj(3,5), objB=objA;


The MiniVectorThe MiniVector

Check the code of the MiniVector– A small version of the Vector Class available in

STL

The MiniVector uses a function called Reserve() to allocate a dynamic array for extra space


The C++ Index Operator [ ]The C++ Index Operator [ ]

. . . ar r [i ] . . .

ar r + iar r

arr[i] = 30;

// arr[i] is the address into which 30 is copied

t = arr[i] + 4;

// add 4 to the value of the element at arr[i]


MatricesMatrices A Matrix is a two-dimensional array that

corresponds to a row-column table of entries of a specified data type.

Matrices are referenced using a pair of indices that specify the row and column location in the table.

8 1 7 - 2

0 - 3 4 6

1 0 - 1 4 1 0

0 1 2 3

01

2

Example:The element mat[0][3] is 2 The element mat[1][2] is 4.


Vectors and MatricesVectors and Matrices

A dynamic Matrix is represented by using the Vector Class.– Visit the matrix.h file

A dynamic Matrix can be described by using dynamic arrays as well. The code is more complex than using vectors.( Think!) - Food for you brain– How would you define a dynamic matrix by using a

dynamic array?


Summary Slide 1Summary Slide 1

§- Pointers contain the address of data in memory…

- Data is accessed by applying the dereference operator *

§- Operators such as +, ++, and += apply to pointers.

§- With such operators, pointers can be used for algorithms involving array traversal, but their primary application is in the allocation and maintenance of dynamic memory.



§- vector implementation- The miniVector class illustrates the key points.1) It allocates dynamic memory using:

destructor copy constructor

overloaded assignment operator

2) It implements push_back(): Therefore it must control vector capacity in

order to minimize dynamic memory reallocation.

3) It allows access to elements by using an index:

Therefore the class implements an overloaded index operator



§- Two dimensional arrays in C++- have the same problems as one-dimensional

arrays:

1) fixed size

2) no size attribute

3) If it is a function argument, it is necessary to specify the number of columns as a constant.

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