Assembly Language for Beginners

1.24. STRUCTURES

struct tm t;

time_t unix_time;

int i;

unix_time=time(NULL);

localtime_r (&unix_time, &t);

for (i=0; i<9; i++)
{
int tmp=((int*)&t)[i];
printf ("0x%08X (%d)\n", tmp, tmp);
};
};

We justcasta pointer to structure to an array ofint’s. And that works! We run the example at 23:51:45
26-July-2014.

0x0000002D (45)
0x00000033 (51)
0x00000017 (23)
0x0000001A (26)
0x00000006 (6)
0x00000072 (114)
0x00000006 (6)
0x000000CE (206)
0x00000001 (1)

The variables here are in the same order as they are enumerated in the definition of the structure:1.333
on page 351.

Here is how it gets compiled:

Listing 1.339: Optimizing GCC 4.8.1

main proc near
push ebp
mov ebp, esp
push esi
push ebx
and esp, 0FFFFFFF0h
sub esp, 40h
mov dword ptr [esp], 0 ; timer
lea ebx, [esp+14h]
call _time
lea esi, [esp+38h]
mov [esp+4], ebx ; tp
mov [esp+10h], eax
lea eax, [esp+10h]
mov [esp], eax ; timer
call _localtime_r
nop
lea esi, [esi+0] ; NOP
loc_80483D8:
; EBX here is pointer to structure, ESI is the pointer to the end of it.
mov eax, [ebx] ; get 32-bit word from array
add ebx, 4 ; next field in structure
mov dword ptr [esp+4], offset a0x08xD ; "0x%08X (%d)\n"
mov dword ptr [esp], 1
mov [esp+0Ch], eax ; pass value to printf()
mov [esp+8], eax ; pass value to printf()
call ___printf_chk
cmp ebx, esi ; meet structure end?
jnz short loc_80483D8 ; no - load next value then
lea esp, [ebp-8]
pop ebx
pop esi
pop ebp
retn
main endp