Dynamic memory allocation in C ? With Example

Dynamic memory allocation in C

The concept of dynamic memory allocation in c language enables the C programmer to allocate memory at runtime. Dynamic memory allocation in c language is possible by 4 functions of stdlib.h header file.

1. malloc()
2. calloc()
3. realloc()
4. free()

Before learning above functions, let's understand the difference between static memory allocation and dynamic memory allocation.

static memory allocation	dynamic memory allocation
memory is allocated at compile time.	memory is allocated at run time.
memory can't be increased while executing program.	memory can be increased while executing program.
used in array.	used in linked list.

Now let's have a quick look at the methods used for dynamic memory allocation.

malloc()	allocates single block of requested memory.
calloc()	allocates multiple block of requested memory.
realloc()	reallocates the memory occupied by malloc() or calloc() functions.
free()	frees the dynamically allocated memory.

1. malloc (Memory Allocation):

Allocates a specified number of bytes of memory.
Syntax: void* malloc(size_t size);

Example:

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

int main() {
    int *arr;
    int i, n;

    // Get the number of elements from the user
    printf("Enter the number of elements: ");
    scanf("%d", &n);

    // Allocate memory for an array of integers
    arr = (int *)malloc(n * sizeof(int));

    // Check if memory allocation was successful
    if (arr == NULL) {
        printf("Memory allocation failed\n");
        return 1; // Exit the program with an error code
    }

    // Input elements from the user
    printf("Enter %d elements:\n", n);
    for (i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    // Display the elements
    printf("Elements entered: ");
    for (i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }

    // Free the allocated memory
    free(arr);

    return 0;
}

Output

yaml
Enter the number of elements: 5
Enter 5 elements:
10 20 30 40 50
Elements entered: 10 20 30 40 50

2. calloc (Contiguous Allocation):

Allocates a specified number of blocks of memory, each with a specified number of bytes.
Syntax: void* calloc(size_t num, size_t size);

Example:

c
int *arr;
arr = (int *)calloc(5, sizeof(int));

3. realloc (Re-allocation):

Changes the size of the memory block previously allocated using malloc or calloc.
Syntax: void* realloc(void* ptr, size_t size);

Example:

c
int *arr;
arr = (int *)malloc(5 * sizeof(int));
arr = (int *)realloc(arr, 10 * sizeof(int));

4. free:

Deallocates the memory block allocated by malloc, calloc, or realloc.
Syntax: void free(void* ptr);
Example:

c
int *arr;
arr = (int *)malloc(5 * sizeof(int));
free(arr);

Remember to check if the allocation was successful by verifying if the returned pointer is not NULL. Also, after using the allocated memory, always free it to avoid memory leaks.