ensure free allocation memory

Question

I asked 8 days ago how to ensure that the memory that I freed is absolutely freed
look at this post
https://www.sololearn.com/Discuss/1812954/?ref=app
Bennett Post told me the correct way to do that but it is to complicated

Answer 1

now I have this simple way to ensure that
check that

https://code.sololearn.com/c64zXgieYFg0/?ref=app

when I free an almost freed memory I will see a runtime error so that the freed memory is really freed

Answer 2

I am sorry I didn't understand 😁

Answer 3

Cluck'n'Coder
you changed p to NULL so you lost the memory that freed .. how to ensure free with that

Answer 4

There's no way to do that in C. Ensuring that freed memory is freed (which is guaranteed by the ANSI / ISO C standards) is about as futile as trying to determine if a string was null terminated or not.

Using a debugger to track allocations and dangling pointers is probably your only option.

Answer 5

Allocated data is tracked by malloc() so your call to free() guarantees the memory pointed to by 'p' is freed.
After the call to free(), 'p' is a dangling pointer so if you want to NULL check it, you'll have to make sure it points to NULL.

Your second call to free() is undefined behavior and will most likely cause memory corruption.

Answer 6

The program you linked to will try to free 'p' twice. It doesn't check that 'p' wasn't already freed.

You do not want to free memory that was not allocated. A good rule of thumb is that for every call to malloc() there should be a call to free() before the program exits.

This is probably what you want:

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

int main(void)
{
int *p = malloc(4 * sizeof(int));
// free(p); <-- Uncomment these two
// p = NULL; <-- and see what happens

if (p != NULL) {
printf("if the memory is not freed you will see me");
free(p);
}

return 0;
}