Introduction to Dynamic Memory Allocation in C: malloc, calloc, and free

In C programming, memory management is a key aspect of efficient coding. Dynamic Memory Allocation (DMA) lets you allocate memory during runtime, giving your program the flexibility to handle variable-size data efficiently.

Let’s explore what DMA is, and how functions like malloc(), calloc(), realloc(), and free() work in real-world examples.

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What is Dynamic Memory Allocation?

Dynamic Memory Allocation allows your program to request memory from the heap at runtime instead of using static memory size.

Useful when:

• The size of data structures is not known beforehand.
• You want to save memory by allocating only what’s needed.

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DMA Functions in C

1. malloc() – Memory Allocation

Allocates a block of memory of specified size (in bytes) and returns a pointer to the first byte.

int *ptr;
ptr = (int*) malloc(5 * sizeof(int));  // Allocates memory for 5 integers

Note: Contents of allocated memory are uninitialized.

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2. calloc() – Contiguous Allocation

Allocates memory for an array of elements and initializes all bytes to zero.

int *ptr;
ptr = (int*) calloc(5, sizeof(int));  // Allocates and initializes 5 integers

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3. realloc() – Reallocate Memory

Changes the size of previously allocated memory.

ptr = realloc(ptr, 10 * sizeof(int));  // Reallocates memory to hold 10 integers

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4. free() – Free Memory

Releases memory back to the system to avoid memory leaks.

free(ptr);  // Always free dynamically allocated memory

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Example Program Using malloc() and free()

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

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

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

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

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

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

    printf("You entered:\n");
    for (i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }

    free(arr);  // Important to prevent memory leaks

    return 0;
}

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malloc vs calloc Comparison

Feature	malloc()	calloc()
Initialization	No (garbage values)	Yes (all values zero)
Syntax	malloc(size)	calloc(num, size)
Speed	Slightly faster	Slightly slower

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Key Takeaways

• Use malloc() or calloc() to allocate memory dynamically.
• Use realloc() to resize allocated memory.
• Always use free() to release memory and avoid leaks.
• Dynamic memory allocation is essential for building flexible and efficient programs.

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Conclusion

Understanding dynamic memory allocation in C allows you to build scalable, memory-efficient applications. Whether it’s working with arrays, structures, or linked lists, using functions like malloc(), calloc(), and free() is crucial for runtime memory control. Practice these concepts to improve your skills in system-level programming.