CODEWITHSUNDEEP
assemblyx86x86-16emu8086
0xmarsh
0xmarsh

Reputation: 51

Work with addresses in assembly

So I can't figure out why my program doesn't work and the different outputs for different input. I have 2 variables: 

   static_num1_ptr    dw 7 ;
   static_num1_ptr_ptr dw [static_num1_ptr];

I have this code: 

    mov     bx,static_num1_ptr_ptr;
    mov     bx,[bx];
    mov     ax,[bx];
    call    print_num

I need to change the declaration of the num1-ptr and num1_ptr_ptr in order to print 7. I can't change the 4 lines of code. I tried changing num1_ptr_ptr to be equal to [num1_ptr] and num1_ptr to be 7. But that gives me 0. Can someone help me understand the logic here? I use emu8086

Upvotes: 2

Views: 526

Answers (1)

Fifoernik
Fifoernik

Reputation: 9899

I can't change the 4 lines of code.

I think the solution lies in closely reading the names of these labels!

If the first label reads static_num1_ptr, it most probably means that it is supposed to be a pointer to num1 and not the value of num1 itself.
You'll need a third line here:

static_num1         dw 7
static_num1_ptr     dw offset static_num1
static_num1_ptr_ptr dw offset static_num1_ptr

Now your 4 lines of code

mov  bx, static_num1_ptr_ptr
mov  bx, [bx]
mov  ax, [bx]
call print_num

will correctly dereference twice ([bx]) and print the value 7.

Upvotes: 3

Related Questions