Dynamic Memory Allocation  

  §  SMA à STATIC MEMORY ALLOCATION

Void main()
{
          Int a;    //SMA
          float;   //SMA
          char x[5];    //SMA
}

  §  DMA  à DNAMIC MEMORY ALLOCATION

o  Dma varibales doesn’t have no name but having only addresses means stored in pointer variable.

o  when we doen’t known how many variables are used in program we used DMA.

Functions used in DMA

  §  malloc()

o  malloc (size of the variable)
o  malloc(6)
means 6 bytes memory create
o  malloc doesn’t required to tells the data type of the memory block which it will create.  

  §  calloc()

  §  realloc()

  §  free()

Malloc function


#include <stdio.h>
#include <stdlib.h>
  
int main()
{
  
    // This pointer will hold the
    // base address of the block created
    int* ptr;
    int n, i, sum = 0;
  
    // Get the number of elements for the array
    n = 5;
    printf("Enter number of elements: %d\n", n);
  
    // Dynamically allocate memory using malloc()
    ptr = (int*)malloc(n * sizeof(int));
  
    // Check if the memory has been successfully
    // allocated by malloc or not
    if (ptr == NULL) {
        printf("Memory not allocated.\n");
        exit(0);
    }
    else {
  
        // Memory has been successfully allocated
        printf("Memory successfully allocated using malloc.\n");
  
        // Get the elements of the array
        for (i = 0; i < n; ++i) {
            ptr[i] = i + 1;
        }
  
        // Print the elements of the array
        printf("The elements of the array are: ");
        for (i = 0; i < n; ++i) {
            printf("%d, ", ptr[i]);
        }
    }
  
    return 0;
}
Output:
Enter number of elements: 5
Memory successfully allocated using malloc.
The elements of the array are: 1, 2, 3, 4, 5,

Free function

#include <stdio.h>
#include <stdlib.h>
  
int main()
{
  
    // This pointer will hold the
    // base address of the block created
    int *ptr, *ptr1;
    int n, i, sum = 0;
  
    // Get the number of elements for the array
    n = 5;
    printf("Enter number of elements: %d\n", n);
  
    // Dynamically allocate memory using malloc()
    ptr = (int*)malloc(n * sizeof(int));
  
    // Dynamically allocate memory using calloc()
    ptr1 = (int*)calloc(n, sizeof(int));
  
    // Check if the memory has been successfully
    // allocated by malloc or not
    if (ptr == NULL || ptr1 == NULL) {
        printf("Memory not allocated.\n");
        exit(0);
    }
    else {
  
        // Memory has been successfully allocated
        printf("Memory successfully allocated using malloc.\n");
  
        // Free the memory
        free(ptr);
        printf("Malloc Memory successfully freed.\n");
  
        // Memory has been successfully allocated
        printf("\nMemory successfully allocated using calloc.\n");
  
        // Free the memory
        free(ptr1);
        printf("Calloc Memory successfully freed.\n");
    }
  
    return 0;
}

Output:

Enter number of elements: 5
Memory successfully allocated using malloc.
Malloc Memory successfully freed.

Memory successfully allocated using calloc.
Calloc Memory successfully freed.

Realloc function

#include <stdio.h>
#include <stdlib.h>
  
int main()
{
  
    // This pointer will hold the
    // base address of the block created
    int* ptr;
    int n, i, sum = 0;
  
    // Get the number of elements for the array
    n = 5;
    printf("Enter number of elements: %d\n", n);
  
    // Dynamically allocate memory using calloc()
    ptr = (int*)calloc(n, sizeof(int));
  
    // Check if the memory has been successfully
    // allocated by malloc or not
    if (ptr == NULL) {
        printf("Memory not allocated.\n");
        exit(0);
    }
    else {
  
        // Memory has been successfully allocated
        printf("Memory successfully allocated using calloc.\n");
  
        // Get the elements of the array
        for (i = 0; i < n; ++i) {
            ptr[i] = i + 1;
        }
  
        // Print the elements of the array
        printf("The elements of the array are: ");
        for (i = 0; i < n; ++i) {
            printf("%d, ", ptr[i]);
        }
  
        // Get the new size for the array
        n = 10;
        printf("\n\nEnter the new size of the array: %d\n", n);
  
        // Dynamically re-allocate memory using realloc()
        ptr = (int*)realloc(ptr, n * sizeof(int));
  
        // Memory has been successfully allocated
        printf("Memory successfully re-allocated using realloc.\n");
  
        // Get the new elements of the array
        for (i = 5; i < n; ++i) {
            ptr[i] = i + 1;
        }
  
        // Print the elements of the array
        printf("The elements of the array are: ");
        for (i = 0; i < n; ++i) {
            printf("%d, ", ptr[i]);
        }
  
        free(ptr);
    }
  
    return 0;
}

Output:

Enter number of elements: 5
Memory successfully allocated using calloc.
The elements of the array are: 1, 2, 3, 4, 5,

Enter the new size of the array: 10
Memory successfully re-allocated using realloc.
The elements of the array are: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,

Calloc Function

#include <stdio.h>
#include <stdlib.h>
  
int main()
{
  
    // This pointer will hold the
    // base address of the block created
    int* ptr;
    int n, i, sum = 0;
  
    // Get the number of elements for the array
    n = 5;
    printf("Enter number of elements: %d\n", n);
  
    // Dynamically allocate memory using calloc()
    ptr = (int*)calloc(n, sizeof(int));
  
    // Check if the memory has been successfully
    // allocated by calloc or not
    if (ptr == NULL) {
        printf("Memory not allocated.\n");
        exit(0);
    }
    else {
  
        // Memory has been successfully allocated
        printf("Memory successfully allocated using calloc.\n");
  
        // Get the elements of the array
        for (i = 0; i < n; ++i) {
            ptr[i] = i + 1;
        }
  
        // Print the elements of the array
        printf("The elements of the array are: ");
        for (i = 0; i < n; ++i) {
            printf("%d, ", ptr[i]);
        }
    }
  
    return 0;
}

Output:

Enter number of elements: 5
Memory successfully allocated using calloc.
The elements of the array are: 1, 2, 3, 4, 5,

**You reached end of lecture**

Your feedback is important for us :)