DS: Memorey allocation

Memorey allocation Functions

1.Static Memorey Allocation

2.Dynamic Memorey Allocation

1.Static Memorey Allocation: If memorey space to be allocated for various variables is decided during compilation time itself, then memorey space can't be expanded to accommodate more data or cannot be reduced to accommodate less data.In this case once the memorey is allocated it is fixed.

Example : array

 

Disadvantages:

1. Leads to underutilization if more memorey space is allocated.

2. Leads to overflow if les memorey is allocated.

2.Dynamic Memorey Allocation:It is a process of allocating memorey space during execution ti,e. This allocation technique uses predefined functions to allocate and release memorey for data during execution time.

Various memorey management functions:

1.malloc

2.calloc

3.realloc

4.free

1.malloc()

This function allocates the memorey during run time.

Syntax:

data_type *p;

p=(data_type*)malloc(size);

Write a program to show the usage of malloc

#include<stdio.h>

void main()

{

int *p1, *p2;

int sum;

p1=(int*)malloc(sizeof(int));

p2=(int*)malloc(sizeof(int));

*p1=10;

*p2=20;

sum=*p1 + *p2;

printf(“sum=%d”,sum);

}

2.calloc()

Allocates the required memorey size during execution timeand automatically initialize memorey with 0's.

Syntax:

data_type *p;

p=(data_type*)calloc(n,size);

What will happen if the following program segment is executed ??

int *ptr;

p=(int*)calloc(5,sizeof(int));

Case 1: if the sufficient memorey is avaliable then memorey is allocated.

Concider the following memorey map:

p=(int*)calloc(5,sizeof(int));

execution of this instruction will allocate the 5 blocks of memorey as the free memorey is avaliable.

Case2: if the sufficient memorey is not avaliable then memorey will not be allocated.

Concider the following memorey map:

 

p=(int*)calloc(5,sizeof(int));

execution of this instruction will return NULL since there is no sufficient memorey is avaliable.

3.realloc()

Changes the memorey size during execution time as required.

Syntax:

data_type *p;

p=(data_type*)calloc(ptr,size);