Variation in Pointer address values

Question

I tested a small program which is written below.My question is why there is a 12 bytes difference between the pointer to a value and a pointer to the first pointer.But if you look at other pointer addresses there is only a difference of 8 bytes every time.I executed this program multiple times and always I see this difference.Can anyone explain me what could be the reason?Thanks in advance..

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

int main(void)
{
        int val;
        int *ptr;
        int **ptrptr;
        int ***ptrptrptr;
        int ****ptrptrptrptr;
        int *****ptrptrptrptrptr;

        val=10;
        ptr=&val;
        ptrptr=&ptr;
        ptrptrptr=&ptrptr;
        ptrptrptrptr=&ptrptrptr;
        ptrptrptrptrptr=&ptrptrptrptr;

        printf("Value-%d\n",val);
        printf("Value address - %d\n",ptr);
        printf("Pointer address - %d\n",ptrptr);
        printf("Pointer Pointer Address -%d\n",ptrptrptr);
        printf("Pointer Pointer Pointer Address -%d\n",ptrptrptrptr);
        printf("Pointer Pointer Pointer Pointer Address -%d\n",ptrptrptrptrptr);

        return 0;
}

The results are:

Value-10
Value address - -1308521884
Pointer address - -1308521896
Pointer Pointer Address --1308521904
Pointer Pointer Pointer Address --1308521912
Pointer Pointer Pointer Pointer Address --1308521920

Whay compiler, what linker, what processor? 32 or 64-bit? What is an int - how big is it? Does it really matter much? I mean, how did you even notice? — Martin James
– Martin James, Commented Apr 28, 2012 at 21:31
It's interesting that changing the first int to long works as you expect. — strkol
– strkol, Commented Apr 28, 2012 at 21:51

cnicutar · Accepted Answer · 2012-04-28 21:29:10Z

4

It's just the stack layout your compiler chose, f.e. it could be for alignment reasons. Things would most likely still work with other layouts.

Side note, you should use %p to print addresses.

answered Apr 28, 2012 at 21:29

cnicutar

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5 Comments

Teja Over a year ago

Yes %p is converting the int address into hexa..hope I am correct.. but still whats the reason for stack taking address like that...

cnicutar Over a year ago

@Vutukuri The stack layout isn't fixed in stone, nor is it standard. Each compiler has absolute freedom in choosing how to arrange local variables. Passing arguments is another story (cdecl, stdcall).

Teja Over a year ago

Okay so u mean to say if I execute the same program on a diff compiler I might get diff results?

cnicutar Over a year ago

@Vutukuri Yup. Also, you might get different results by simply changing the switches - for example optimization flags.

Kerrek SB Over a year ago

@Vutukuri: if you use %p, then you must cast your pointer to void*. If you want to print an integral value, you can also cast to uintptr_t and use the appropriate macro from stdint.h.

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