Here is a fun one related to this module\'s topics, pointers and memory allocati

Question

Here is a fun one related to this module's topics, pointers and memory allocation. It just popped up in a forum I monitor (I won't reveal which one here because I want you to dig out the answer yourself.

The writer says:

I encountered this question during discussion with interviewer -

If I have allocated 4 bytes of memory from malloc.

int *p = (int*) malloc(4);

now if I moved pointer by 4 byte.

P++;

And now pointer is pointing memory which is out of 4 byte of memory allocated by malloc. Let's assume that this memory has permission to read-write.

*p=4; That means pointer is going out of allocated memory.

Now consider a case where I allocated some memory but whenever my pointer moves out of allocated and write on that memory then I want to be informed but how??

I have only malloc and free to use.

Please give a written explanation only

Explanation / Answer

We have following code:

#include<stdio.h>

void main()
{
   int* p = (int*) malloc(4); //here p is a pointer that point to memory location of 4 bytes
   p++; //now pointer is pointing memory which is out of 4 byte of memory allocated by malloc
   *p =4;
   printf("%d", *p); //it will print the value as 4
}

now if we use const pointer in place of normal pointer then we can avoid going out of 4 byte of memory allocated by malloc as given below:

#include<stdio.h>

void main()
{
   int* const p = (int*) malloc(4); //here p is a pointer that point to memory location of 4 bytes
   p++; //p++ is not possible now
}

According to me, this much we can do, because accessing memory outside the malloc is not desirable and we can have a chance of memory leak also. Which is not a good programing practice

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