How to Release Memory in C?
In C programming, releasing memory means deallocating memory that was previously allocated dynamically using functions like malloc(), calloc(), or realloc(). In this article, we will learn how to release memory in C.
Free Dynamic Memory in C
To release the dynamically allocated memory, we can use the free() function in C. The free function takes a pointer as an argument that points to the memory block allocated by the malloc(), calloc(), or realloc() functions and deallocates the memory making it available for reuse.
Syntax of free()
free(ptr);
here,
- ptr is the pointer that points to the dynamically allocated memory block.
Note: Static memory (i.e. memory allocated on the stack) cannot be deleted by the user.
C Program to Release Allocated Memory
The following program illustrates how we can release memory in C using free() function:
// C Program to release dynamically allocated memory
#include <stdio.h>
#include <stdlib.h>
int main()
{
/* ____ Release memory for an integer ______ */
// Allocate memory for a single integer
int* ptr_single = (int*)malloc(sizeof(int));
if (ptr_single == NULL) {
printf("Memory allocation failed\n");
return 1;
}
// Use the allocated memory for a single variable
*ptr_single = 42;
printf("Value of variable: %d\n", *ptr_single);
// Release the memory allocated for the single variable
free(ptr_single);
printf("Memory for variable released\n");
// Set the pointer to NULL to avoid dangling pointers
ptr_single = NULL;
/* ____ Release memory for a dynamically allocated array
* ______ */
// Allocate memory for an array of integers
int* ptr_array = (int*)malloc(5 * sizeof(int));
if (ptr_array == NULL) {
printf("Memory allocation failed\n");
return 1;
}
// Use the allocated memory for an array
for (int i = 0; i < 5; i++) {
ptr_array[i] = i;
}
printf("Array elements:");
for (int i = 0; i < 5; i++) {
printf("%d ", ptr_array[i]);
}
// Release the memory allocated for the array
free(ptr_array);
printf("\nMemory for array released\n");
// Set the pointer to NULL to avoid dangling pointers
ptr_array = NULL;
return 0;
}
Output
Value of variable: 42 Memory for variable released Array elements:0 1 2 3 4 Memory for array released
Time Complexity: O(1), here denotes the number of elements in the array.
Auxiliary Space: O(1)