Since C is a structured language, it has some fixed rules for programming. One of them includes changing the size of an array. An array is a collection of items stored at contiguous memory locations.
As it can be seen that the length (size) of the array above made is 9. But what if there is a requirement to change this length (size). For Example, If there is a situation where only 5 elements are needed to be entered in this array. In this case, the remaining 4 indices are just wasting memory in this array. So there is a requirement to lessen the length (size) of the array from 9 to 5.
This procedure is referred to as Dynamic Memory Allocation in C. Therefore, C Dynamic Memory Allocation can be defined as a procedure in which the size of a data structure (like Array) is changed during the runtime. C provides some functions to achieve these tasks. There are 4 library functions provided by C defined under <stdlib.h> header file to facilitate dynamic memory allocation in C programming. They are:
- malloc()
- calloc()
- free()
- recalloc()
The “malloc” or “memory allocation” method in C is used to dynamically allocate a single large block of memory with the specified size. It returns a pointer of type void which can be cast into a pointer of any form. It doesn’t Initialize memory at execution time so that it has initialized each block with the default garbage value initially.
ptr = (cast-type*) malloc(byte-size)
ptr = (int*) malloc(100 * sizeof(int));
Since the size of int is 4 bytes, this statement will allocate 400 bytes of memory. And, the pointer ptr holds the address of the first byte in the allocated memory.
#include <stdio.h>
#include <stdlib.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
int main()
{
int n,i;
char x='A';
printf("Enter the no of items to be entered:");
scanf("%d",&n);
char *ptr=(char*)malloc(n*1);
for(i=0;i<n;i++)
{
*ptr=x ;
x++;
printf("Item-%c,Memory address-%d\n",*ptr,ptr);//ptr is prnting the memory address of x
ptr++;//increments the memmry adress of x
}
}
