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DynamicObjects

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Memory Management

Static Memory Allocation

Memory is allocated at compilation time

Dynamic Memory

Memory is allocated at running time

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Static vs. Dynamic Objects

Static object

(variables as declared in function calls)

Memory is acquired

automatically

Memory is returned

automatically when object

goes out of scope

Dynamic object

Memory is acquired by

program with an allocation

request newoperation

Dynamic objects can exist

beyond the function in which

they were allocated

Object memory is returned by

a deallocation request

deleteoperation

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Memory Allocation

{int a[200];

}

int* ptr;

ptr = new int[200];

delete [] ptr;

new

delete

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Object (variable) creation:New

Syntaxptr = new SomeType;

where ptris a pointer of type SomeType

p

Uninitialized int variable

Example

int* p = new int;

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Object (variable) destruction: Delete

Syntax

delete p;

storage pointed to by p is returned to free store and p is now undefined

p

Exampleint* p = new int;

*p = 10;

delete p;

10

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Array of New:

dynamic arrays

Syntax

P = new SomeType[Expression];

Where Pis a pointer of type SomeType

Expressionis the number of objects to be

constructed -- we are making an array

Because of the flexible pointer syntax, Pcan be

considered to be an array

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Example

Dynamic Memory Allocationn Request for unnamedmemory from the Operating System

n int *p, n=10;

p = new int;

p = new int[100];

p

new

p

new

p = new int[n]; p

new

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Memory Allocation Example

Want an array of unknown size#include

using namespace std;

void main()

{

int n;

cout > n;

int *grades = new int[n];

for(int i=0; i < n; i++){

int mark;

cout

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Freeing (or deleting) Memory

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A Simple Dynamic List Example

cout > n;

int *A = new int[n];

if(n

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Initialize

void initialize(int list[], int size, int value){

for(int i=0; i

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print()

void print(int list[], int size) {

cout

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Adding Elements

// for adding a new element to end of array

int* addElement(int list[], int& size, int value){

int* newList = new int [size+1]; // make new array

if(newList==0){

cout

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Adding Element (version 2)

// for adding a new element to end of array

// here list is a reference to a pointer variable: if the value ofthe pointer is changed in function, the change is global.

void addElement( int * & list, int & size, const int value ){

int * newList = new int [size + 1];

if( newList == NULL ){

cout

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Deleting Element (version 2)

void deleteFirst( int * & list, int & size ){

if( size

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Another Main program

int main(){

int * A = NULL;

int size = 0;

int i;

for( i = 0; i < 10; i++ )

addElement( A, size, i );

for( i = 0; i < 10; i++ )

cout

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Dangling Pointer Problem

int *A = new int[5];

for(int i=0; i

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Memory Leak Problem

int *A = new int [5];

for(int i=0; i

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A Dynamic 2D Array

A dynamic array isan array of pointersto save space whennot all rows of thearray are full.

int **table;

32 18 2412

42 141912161113

1811

13 1413

22

table = new int*[6];

table[0] = new int[4];

table[1] = new int[7];

table[2] = new int[1];

table[3] = new int[3];

table[4] = new int[2];

table[5] = NULL;

table[0]

table[1]

table[2]

table[3]

table[4]

table[5]

table

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Memory Deallocation

Memory leak is a serious bug!

Each row must be deleted individually

Be careful to delete each row before deletingthe table pointer.

for(int i=0; i

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int m, n;

cin >> m >> n >> endl;

int** mat;

mat = new int*[m];

for (int i=0;i> m >> n >> endl;

int** mat;

mat = imatrix(m,n);

int** imatrix(nr, nc) {

int** m;m = new int*[nr];

for (int i=0;i