c - Conversion of integer pointer to integer

Question

Tried following code to check what happens when we convert integer pointer to a integer .

 #include<stdio.h>
 #include<stdlib.h>
 int main()
 {
         int *p;
         int a;
         p = (int *)malloc(sizeof(int));
         *p = 10;
         a = (int)p;
         printf("%d
",*p);
         printf("%d 
",a);
         return 0;
 }

 The output is : 10
                 135680008

Can anyone explain, the concept related to this conversion? Any links provided related to this topic would also be helpful.

Answer 1

Apparently you confuse the pointer with the content of the pointer.

As an analogy to the real world, you could say that, with me pointing at a bird, you want to convert my index finger to a bird. But there is no relation between the type 'bird' and 'finger'.

Transferring that analogy to your program: you are converting the object pointing to your int to an int itself. Since a C pointer is implemented as 'the number of a memory cell', and since there are lots of memory cells available, it's obvious that (int)p will result in a very big number.

Casting is a nasty thing. It's a coincidence that pointers are quite analogous to integers. If they were implemented as "the n^th address of the m^th memory bank", you wouldn't be asking this question because there wouldn't have been an obvious relation, and you wouldn't have been able to do this cast.