Introduction to Programming Lecture 24

Today’s Agenda Memory Allocation Dynamic memory allocation Advantages/disadvantages of Dynamic and static memory allocation Common programming errors while using Dynamic memory allocation

Static Memory Allocation int i , j , k ; char s [ 20 ] ;

Compile Time Allocation

Dynamic Memory Allocation

Heap

Pointers

void Pointer

int *i ; char *s ; i is a pointer to an integer

void *ptr ;

Cast

void *ptr ;

( int * ) ptr ;

NULL

calloc ( n , m ) ; Space in terms of numbers of elements Space in terms of size each of elements

calloc ( 1000 , sizeof ( int ) ) ;

( int * ) calloc ( 1000 , sizeof ( int ) ) ;

void * calloc ( size_t n , size_t el-size ) ;

Example 1 int *iPtr ; iPtr = ( int * ) calloc ( 1000 , sizeof ( int ) ) ; if ( iPtr == NULL ) exit ( ) ;

Number of bytes required void * malloc ( n ) ; Number of bytes required

malloc (1000 *sizeof ( int ) ) ) ;

malloc ( n ( sizeof ( float ) ) ) ;

Static Memory Allocation #define MAXSTUDENT 100 int Student [ MAXSTUDENT ] ;

Problem statement Find the average age of the students in your class

Example 2 int numstd ; int *iPtr , *sPtr ; cout << "Enter the number of students " << endl ; cin >> numstd ; iPtr = malloc ( numstd * ( sizeof ( int ) ) ) ; if ( iPtr == NULL ) {         cout << "Error on malloc " ;         return 1 ;         /* Use a nonzero return to indicate an error has occurred */ } // a while loop to read the ages of the student and place them in the memory sPtr = iPtr ; sPtr++ ;

free ( iPtr ) ;

realloc(void *iPtr, size_t size);

Unreferenced Memory

Memory Leaks

Example main ( ) { funct ( ) ; } funct ( ) int *iPtr ; iPtr = malloc ( 1000 * ( sizeof ( int ) ) ) ; // used the memory

Dangling Pointers

Example int *ptr1 , *ptr2 ; ptr1 = malloc (1000 * ( sizeof ( int ) ) ) ; ptr2 = ptr1 ; - - - free ( ptr1 ) ;

Multi-tasking

Review Dynamic Memory Allocation Efficient usage of computers resources Have to do memory management