Dynamic memory allocation

Dynamic Memory Allocation
Subject : C Language
Name : Uttam Verma

SYNOPSIS
• Memory allocation
• Static MemoryAllocation
• Memory Allocation Process
• Memory Allocation Functions
• Allocation A Block Of Memory :Malloc
• Allocation A Block Of Memory :Calloc
• Altering The Size Of A Block :Realloc
• Releasing The Used Space: Free

MEMORYALLOCATION
• The blocks of information in a memory system is called memory
allocation.
• To allocate memory it is necessary to keep in information of
available memory in the system. If memory management system
finds sufficient free memory, it allocates only as much memory as
needed, keeping the rest available to satisfy future request.
• Memory allocation has two types. They are static and dynamic
memory allocation.

STATIC MEMORY ALLOCATION
• In static memory allocation, size of the memory may be required
and that must be defined before loading and executing the program.
DYNAMIC MEMORYALLOCATION
• In the dynamic memory allocation, the memory is allocated to a
variable or program at the run time.
• The only way to access this dynamically allocated memory is
through pointer.

ALLOCATION A BLOCK OF MEMORY:
MALLOC
malloc() function is used for allocating block of memory at
runtime. This function reserves a block of memory of given
size and returns a pointer of type void.
Ptr=(cast-type*) malloc (byte-size);

EXAMPLE PROGRAM
Output:
Enter the emp details
eno 1
ename priya
esal 10,000
#include <stdio.h>
#include <stdlib.h>
struct emp
{
int eno;
char name;
float esal;
void main()
{
struct emp *ptr;
ptr = (struct emp *) malloc(size of(structemp));
if(ptr == null)
{
pintf(“out of memory”);
}
else
{
printf(“Enter the emp deitals”);
scanf(“%d%s%f,&ptr-> eno,ptr-> name,&ptr-> esal”);
return 0;
}

ALLOCATION A BLOCK OF MEMORY:
CALLOC
calloc() is another memory allocation function that is used for
allocating memory at runtime. calloc function is normally used for
allocating memory to derived data types such as arrays and
structures.
Ptr=(cast-type*)calloc(n,elem-size);

EXAMPLE PROGRAM
output:
Number of elements to be entered :3
Enter 3 numbers:
22
55
14
The numbers entered are :22 55 14
#include <stdio.h>
#include <stdlib.h>
int main()
{
int i, n;
int *a;
printf("Number of elements to be entered:");
scanf("%d",&n);
a = (int*)calloc(n, sizeof(int));
printf("Enter %d numbers:n",n);
for( i=0 ; i < n ; i++ )
{
scanf("%d",&a[i]);
}
printf("The numbers entered are: ");
for( i=0 ; i < n ; i++ )
{
printf("%d ",a[i]);
}
free( a );
return(0);
}

ALTERING THE SIZE OF A BLOCK :REALLOC
realloc() changes memory size that is already allocated
dynamically to a variable.
ptr=REALLOC(ptr,new size);

EXAMPLE PROGRAM
Output:
10 20 30
#include <stdio.h>
#include <stdlib.h>
int main()
{
int *ptr = (int *)malloc(sizeof(int)*2);
int i;
int *ptr_new;
*ptr = 10;
*(ptr + 1) = 20;
ptr_new = (int *)realloc(ptr, sizeof(int)*3);
*(ptr_new + 2) = 30;
for(i = 0; i < 3; i++)
printf("%d ", *(ptr_new + i));
return 0;
}

RELEASING THE USED SPACE: FREE
Free() function should be called on a pointer that was used either with
”calloc()” or “malloc()”,otherwise the function will destroy the memory
management making a system to crash.
free (ptr)

EXAMPLE:
#include<stdio.h>
int main()
{
int *str;
-------
-------
free(str);
}

Dynamic memory allocation

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