Memory & Systems

C Program for Dynamic Memory Allocation (malloc, realloc, free)

Demonstrates safe dynamic heap memory allocation in C, resizing buffers with realloc, and avoiding memory leaks with free().

C Source Code

Editable code sample with line numbers

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

int main(void) {
    int initial_capacity = 3;
    int *numbers = (int *)malloc(initial_capacity * sizeof(int));
    if (numbers == NULL) {
        fprintf(stderr, "Heap memory allocation failed!\n");
        return 1;
    }

// Populate initial items
    for (int i = 0; i < initial_capacity; i++) {
        numbers[i] = (i + 1) * 10;
    }

printf("Initial array (%d elements): ", initial_capacity);
    for (int i = 0; i < initial_capacity; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");

// Expand buffer to 6 elements
    int new_capacity = 6;
    int *expanded = (int *)realloc(numbers, new_capacity * sizeof(int));
    if (expanded == NULL) {
        free(numbers);
        fprintf(stderr, "Heap reallocation failed!\n");
        return 1;
    }
    numbers = expanded;

// Populate newly allocated slots
    for (int i = initial_capacity; i < new_capacity; i++) {
        numbers[i] = (i + 1) * 10;
    }

printf("Resized array (%d elements): ", new_capacity);
    for (int i = 0; i < new_capacity; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");

// Clean up heap allocation to prevent leaks
    free(numbers);
    numbers = NULL;

printf("Memory successfully freed.\n");
    return 0;
}

Expected Output

When this program is compiled and executed, the terminal outputs:

Initial array (3 elements): 10 20 30 
Resized array (6 elements): 10 20 30 40 50 60 
Memory successfully freed.

How the Code Works

Dynamic memory is allocated on the heap using malloc(). When increasing buffer capacity, realloc() copies existing data to a new block if necessary and frees the old block. Always store the return value of realloc() in a temporary pointer first so original memory is not leaked if realloc fails. Freeing with free() and setting the pointer to NULL prevents dangling pointer bugs.

Time Complexity

O(N) for reallocation/copying

Space Complexity

O(N) heap memory

Key Takeaways & Best Practices

Always verify malloc/realloc return values are not NULL.
Always pair malloc with free() to eliminate memory leaks.
Assign freed pointers to NULL to guard against use-after-free bugs.

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Runnable Code

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How the Code Works

Time Complexity

O(N) for reallocation/copying

Space Complexity

O(N) heap memory

Key Takeaways & Best Practices

Always verify malloc/realloc return values are not NULL.
Always pair malloc with free() to eliminate memory leaks.
Assign freed pointers to NULL to guard against use-after-free bugs.

C Program for Dynamic Memory Allocation (malloc, realloc, free)

C Source Code

Expected Output

How the Code Works

Key Takeaways & Best Practices

Master C with ZenCompiler

Related C Examples

C Program to Check Prime Number

C Program to Reverse a String Using Pointers

Python Program to Check Prime Number

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C Program for Dynamic Memory Allocation (malloc, realloc, free)

C Source Code

Expected Output

How the Code Works

Key Takeaways & Best Practices

Master C with ZenCompiler

Related C Examples

C Program to Check Prime Number

C Program to Reverse a String Using Pointers

Python Program to Check Prime Number