Impara Dynamic Memory Allocation | Dynamic Allocation and Multi-level Pointers

In C, arrays usually have a fixed size, meaning their length must be known at compile time. However, sometimes you need an array whose size is determined at runtime, for example, when reading user input or handling variable-sized data. This is where dynamic memory allocation comes in.

You can use functions from <stdlib.h> like malloc() or calloc() to allocate memory for arrays on the heap instead of the stack. This allows you to create arrays with flexible sizes that can grow or shrink as needed.

main.c


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

int main() {
    int n;
    printf("Enter number of elements: ");
    scanf("%d", &n);

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

    if (arr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }

    // Assign values
    for (int i = 0; i < n; i++)
        arr[i] = i + 1;

    // Print values
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);

    // Free allocated memory
    free(arr);
    return 0;
}

Here, malloc() allocates a block of memory large enough to hold n integers. Always check if the pointer returned by malloc() is NULL, it means the allocation failed. After use, free the memory with free() to prevent leaks.

Note

Always pair every malloc() or calloc() with a corresponding free() to avoid memory leaks and wasted system resources.

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Sezione 3. Capitolo 2

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Suggested prompts:

What is the difference between malloc() and calloc() in C?

Can you show an example of how to use malloc() to create a dynamic array?

Why is it important to use free() after allocating memory dynamically?