C Dynamic Memory Allocation - malloc, calloc, realloc, free

🚀 C Dynamic Memory Allocation

In C, **dynamic memory allocation** allows you to allocate memory at runtime instead of compile time. It gives you control over how much memory to use and when to release it.

The standard library provides these functions from <stdlib.h>:

malloc() – Allocates memory block
calloc() – Allocates and initializes memory
realloc() – Resizes memory block
free() – Frees allocated memory

📝 Example: Using malloc()

Allocate memory for 5 integers dynamically using malloc().

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

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

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

    if (arr == NULL) {
        printf("Memory not allocated.\n");
        return 1;
    }

    for (i = 0; i < 5; i++) {
        arr[i] = i + 1;
    }

    printf("Array elements: ");
    for (i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }

    free(arr);
    return 0;
}

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📝 Example: Using calloc()

calloc() also allocates memory, but initializes all values to 0.

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

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

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

    if (arr == NULL) {
        printf("Memory not allocated.\n");
        return 1;
    }

    printf("Array elements (initialized to 0): ");
    for (i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }

    free(arr);
    return 0;
}

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📝 Example: Using realloc()

realloc() is used to resize an already allocated memory block.

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

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

    arr = (int*) malloc(3 * sizeof(int));

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

    for (i = 0; i < 3; i++) {
        arr[i] = i + 1;
    }

    arr = (int*) realloc(arr, 5 * sizeof(int));
    if (arr == NULL) {
        printf("Reallocation failed.\n");
        return 1;
    }

    arr[3] = 4;
    arr[4] = 5;

    printf("Resized array: ");
    for (i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }

    free(arr);
    return 0;
}

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⚠️ Don’t Forget to Free Memory

Whenever you use malloc(), calloc(), or realloc(), remember to use free() after you’re done. It avoids memory leaks.

📌 Summary

malloc(size) → allocates raw memory
calloc(n, size) → allocates and initializes memory to 0
realloc(ptr, newSize) → resizes memory block
free(ptr) → releases memory

🎯 Try This!

Create a program that dynamically allocates memory for a list of names using char**. Resize the list as needed using realloc()!