malloc, calloc , realloc and free

Dynamic Memory Allocation

"stdlib.h" header file include in your program.

malloc()

malloc stands for "memory allocation".

It allocate space in memory at run time according to given size.

It allocate space in single block.

Syntax

ptr = (cast-type*) malloc(byte-size);

NOTE: In above syntax ptr is a pointer type variable.

NOTE: If malloc() allocate space then it return pointer otherwise NULL.

free()

It is used to release run time allocated memory. It means free() can frees occupied memory of malloc() or calloc().

Syntax

free(ptr);

Program

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>

void main(){
int n,i,*ptr,sum=0;
clrscr();
printf("\nEnter number of elements: ");
scanf("%d",&n);
ptr=(int*)malloc(n*sizeof(int));
if(ptr==NULL)
{
printf("\nSorry! Number of element has not given by you.");
exit(0);
}
for(i=0;i< n;i++)
{
printf("\nEnter elements of array: ");
scanf("%d",ptr+i);
}
for(i=0;i< n;i++)
{ printf("\n given element: %d",*(ptr+i));
sum = sum + *(ptr+i);
}
printf("\n Sum=%d",sum);
free(ptr);
getch();
}

See Output

calloc()

calloc stands for "contiguous allocation".

calloc() allocates multiple block of memory.

Difference between malloc() and calloc():- malloc() allocates single block of memory but calloc() allocates multiple block of memory.

Syntax

ptr = (cast-type*)calloc(n, element-size);

Program

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>

void main(){
int n,i,*ptr,sum=0;
clrscr();
printf("\nEnter number of elements: ");
scanf("%d",&n);
ptr=(int*)calloc(n, sizeof(int));
if(ptr==NULL)
{
printf("\nSorry! Number of element has not given by you.");
exit(0);
}
for(i=0;i< n;i++)
{
printf("\nEnter elements of array: ");
scanf("%d",ptr+i);
}
for(i=0;i< n;i++)
{ 
printf("\n given element: %d",*(ptr+i));
sum = sum + *(ptr+i);
}
printf("\n Sum=%d",sum);
free(ptr);
getch();
}

See Output

realloc()

If calloc() or malloc() allocated memory is not sufficient for requirement then we can change size of memory by realloc() at run time.

Here, ptr is reallocated with size of newsize.

Syntax

ptr =(cast-type*)realloc(ptr, newsize);

Program

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>

void main(){
int n1,n2,i,*ptr,sum=0,newSum=0;
clrscr();
printf("\nEnter size of array: ");
scanf("%d",&n1);
ptr=(int*)malloc(n1 * sizeof(int));
if(ptr==NULL){
printf("\nSorry! Number of element has not given by you.");
exit(0);
}
for(i=0;i< n1;i++){
printf("\nEnter elements of array: ");
scanf("%d",ptr+i);
}
for(i=0;i< n1;i++){
printf("\n given element: %d",*(ptr+i));
sum = sum + *(ptr+i);
}
printf("\n Sum=%d",sum);
printf("\nEnter new size of array: ");
scanf("%d",&n2);
ptr = (int *)realloc(ptr, n2);
for(i=0;i< n2;i++){
printf("\nEnter new elements of array: ");
scanf("%d",ptr+i);
}
for(i=0;i< n2;i++){
printf("\n given new element: %d",*(ptr+i));
newSum = newSum + *(ptr+i);
}
printf("\n New Sum=%d",newSum);
free(ptr);
getch();
}

See Output

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