Allocating Memory Dynamically

Dynamic Memory Allocation

• Dynamic memory allocation in C allows for the allocation and deallocation of memory during runtime

• In C, dynamic memory allocation is performed using the functions malloc, calloc, and realloc from the <stdlib.h> header.

• These functions allow you to allocate memory dynamically during program execution.

Here's how each function is used:

malloc

• The malloc function is used to allocate a block of memory of a specified size.
• It takes the number of bytes to allocate as its argument and returns a pointer to the beginning of the allocated memory block.
• The memory allocated by malloc is uninitialized, meaning its contents are undefined.

Example

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

int main() {
    int* dynamicArray = malloc(5 * sizeof(int)); // Allocate memory for an array of 5 integers

    if (dynamicArray == NULL) {
        printf("Failed to allocate memory.\n");
        return 1; // Error handling
    }

    // Use the dynamically allocated memory

    free(dynamicArray); // Deallocate the memory when done

    return 0;
}

calloc

• The calloc function is used to allocate a block of memory for an array of a specified number of elements, each with a specified size.
• It takes two arguments: the number of elements and the size of each element.
• calloc initializes the allocated memory block to zero.

Example

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

int main() {
    int* dynamicArray = calloc(5, sizeof(int)); // Allocate memory for an array of 5 integers

    if (dynamicArray == NULL) {
        printf("Failed to allocate memory.\n");
        return 1; // Error handling
    }

    // Use the dynamically allocated memory

    free(dynamicArray); // Deallocate the memory when done

    return 0;
}

realloc

• The realloc function is used to resize an already allocated memory block.
• It takes two arguments: a pointer to the previously allocated memory block and the new size in bytes.
• realloc may move the memory block to a different location if necessary.
• If the reallocation fails, realloc returns NULL and the original memory block remains unchanged.

Example

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

int main() {
    int* dynamicArray = malloc(5 * sizeof(int)); // Allocate memory for an array of 5 integers

    if (dynamicArray == NULL) {
        printf("Failed to allocate memory.\n");
        return 1; // Error handling
    }

    // Use the dynamically allocated memory

    dynamicArray = realloc(dynamicArray, 10 * sizeof(int)); // Resize the array to 10 integers

    if (dynamicArray == NULL) {
        printf("Failed to reallocate memory.\n");
        return 1; // Error handling
    }

    // Use the resized memory block

    free(dynamicArray); // Deallocate the memory when done

    return 0;
}

NULL and FREE

• After dynamically allocating memory, it's important to check if the allocation was successful by verifying if the returned pointer is NULL.

• If it is NULL, it indicates that the allocation failed due to insufficient memory.

• Remember to deallocate dynamically allocated memory using the free function when it's no longer needed to avoid memory leaks.