C free() method
“free” method in C is used to dynamically de-allocate the memory. The memory allocated using functions malloc() and calloc() is not de-allocated on their own. Hence the free() method is used, whenever the dynamic memory allocation takes place. It helps to reduce wastage of memory by freeing it.
Syntax of free() in C
free(ptr);
Example of free() in C
C
#include <stdio.h>#include <stdlib.h>int main(){ // This pointer will hold the // base address of the block created int *ptr, *ptr1; int n, i; // Get the number of elements for the array n = 5; printf("Enter number of elements: %d\n", n); // Dynamically allocate memory using malloc() ptr = (int*)malloc(n * sizeof(int)); // Dynamically allocate memory using calloc() ptr1 = (int*)calloc(n, sizeof(int)); // Check if the memory has been successfully // allocated by malloc or not if (ptr == NULL || ptr1 == NULL) { printf("Memory not allocated.\n"); exit(0); } else { // Memory has been successfully allocated printf("Memory successfully allocated using malloc.\n"); // Free the memory free(ptr); printf("Malloc Memory successfully freed.\n"); // Memory has been successfully allocated printf("\nMemory successfully allocated using calloc.\n"); // Free the memory free(ptr1); printf("Calloc Memory successfully freed.\n"); } return 0;} |
Enter number of elements: 5 Memory successfully allocated using malloc. Malloc Memory successfully freed. Memory successfully allocated using calloc. Calloc Memory successfully freed.
Dynamic Memory Allocation in C using malloc(), calloc(), free() and realloc()
Since C is a structured language, it has some fixed rules for programming. One of them includes changing the size of an array. An array is a collection of items stored at contiguous memory locations.
As can be seen, the length (size) of the array above is 9. But what if there is a requirement to change this length (size)? For example,
- If there is a situation where only 5 elements are needed to be entered in this array. In this case, the remaining 4 indices are just wasting memory in this array. So there is a requirement to lessen the length (size) of the array from 9 to 5.
- Take another situation. In this, there is an array of 9 elements with all 9 indices filled. But there is a need to enter 3 more elements in this array. In this case, 3 indices more are required. So the length (size) of the array needs to be changed from 9 to 12.
This procedure is referred to as Dynamic Memory Allocation in C.
Therefore, C Dynamic Memory Allocation can be defined as a procedure in which the size of a data structure (like Array) is changed during the runtime.
C provides some functions to achieve these tasks. There are 4 library functions provided by C defined under <stdlib.h> header file to facilitate dynamic memory allocation in C programming. They are:
- malloc()
- calloc()
- free()
- realloc()
Let’s look at each of them in greater detail.