How to deallocate memory without using free method in C Language?

Need for realloc() method

Realloc ( realloc() method ) returns a pointer to a new object with the size provided by size and deallocates the old object referenced to by ptr. Prior to deallocation, the contents of the new object are identical to those of the old object, up to the smaller of the new and old sizes. Any bytes in the new object that are larger than the old object's size have uncertain values.

For Example:

/* code with memory leak */
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
    int *ptr = (int*)malloc(10);
    return 0;
}

You can also try this code with Online C Compiler

Run Code

Result: On Checking the memory leak with the Valgrind tool, 10 bytes of memory are leaked, highlighted in red.

 [akash@ubuntu]$ valgrind –leak-check=full ./free
  ==1238== LEAK SUMMARY:
  ==1238== definitely lost: 10 bytes in 1 blocks. //Memory Leak
  ==1238== possibly lost: 0 bytes in 0 blocks.
  ==1238== still reachable: 0 bytes in 0 blocks.
  ==1238== suppressed: 0 bytes in 0 blocks.
[akash@ubuntu]$

Now, we will be modifying the above code using the realloc() method.

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
    int *ptr = (int*) malloc(10);
    //realloc is being called with size = 0
    realloc(ptr, 0);
    return 0;
}

You can also try this code with Online C Compiler

Run Code

Result: Examine the Valgrind output. No memory leaks are conceivable, as shown by the red hue.

  [akash@ubuntu]$ valgrind –leak-check=full ./a.out
  ==1435== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 11 from 1)
  ==1435== malloc/free: in use at exit: 0 bytes in 0 blocks.
  ==1435== malloc/free: 1 allocs, 1 frees, 10 bytes allocated.
  ==1435== For counts of detected errors, rerun with: -v
  ==1435== All heap blocks were freed — no leaks are possible. // No leak
  [akash@ubuntu]$

Frequently Asked Questions

What are the uses of realloc () and free () methods?

The main function of realloc() is that it is used to change the size of previously allocated space. On the other hand, the free() method deallocates the previously allocated space.

Is it better to use malloc () or calloc ()?

The calloc method sets the allocated memory to 0, whereas malloc does not. As a result, the junk data is stored in the memory allocated by malloc. In other words, calloc is the result of combining malloc with memeset.

Conclusion

In this article, we have extensively discussed the memory de-allocation without using the free() method in C language.

We hope this blog has helped you enhance your knowledge regarding the realloc() method in C language. Some official documentation on big data that can help you improve your understanding is C #ifndef and Dynamic Memory Allocation.