C Reallocate Memory

✅ C Reallocate Memory `realloc()`?

In C Reallocate Memory The function realloc() is used to change the size of memory that was allocated using malloc() or calloc().

It can:

Increase the memory block size
Decrease the memory block size
Move the memory block to a new location (if needed)

📌 Syntax

Where:

pointer → existing allocated memory
new_size → new required size in bytes

🧠 Important Behavior Notes

Action	Behavior
Increase size	Keeps previous data and adds new space (uninitialized).
Decrease size	Keeps only the data that fits.
Memory move	If resizing requires a new block, old data is copied automatically.
Failure	Returns `NULL` — original pointer remains unchanged.

🔍 Example: Expanding an Array Dynamically

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

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

arr[0] = 10;
arr[1] = 20;
arr[2] = 30;

// Resize to store 5 integers
arr = (int*) realloc(arr, 5 * sizeof(int));

arr[3] = 40;
arr[4] = 50;

for (int i = 0; i < 5; i++)
printf("%d ", arr[i]);

free(arr);
return 0;
}

#include <stdio.h>

#include <stdlib.h>

int main() {

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

arr[0] = 10;

arr[1] = 20;

arr[2] = 30;

// Resize to store 5 integers

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

arr[3] = 40;

arr[4] = 50;

for (int i = 0; i < 5; i++)

printf("%d ", arr[i]);

free(arr);

return 0;

}

Output:

❗ Safe Usage of `realloc()` (Recommended Method)

To avoid memory loss if realloc() fails:

📍 Example: Safe Reallocation

🧹 Remember to Free Memory

Always call:

when you are done using dynamically allocated memory.

🧾 Key Points to Remember

realloc() resizes memory previously allocated with malloc() or calloc().
It preserves existing data automatically.
It can move memory to a new location if needed.
Always check if realloc() returns NULL before assigning.
Always free() memory after use.

C Reallocate Memory