1.24. STRUCTURES
lea eax, [esp+10h]
mov [esp], eax ; timer
call _localtime_r
lea esi, [esi+0] ; NOP
; ESI here is the pointer to structure in local stack. EDI is the pointer to structure end.
loc_8048408:
xor ebx, ebx ; j=0
loc_804840A:
movzx eax, byte ptr [esi+ebx] ; load byte
add ebx, 1 ; j=j+1
mov dword ptr [esp+4], offset a0x02x ; "0x%02X "
mov dword ptr [esp], 1
mov [esp+8], eax ; pass loaded byte to printf()
call ___printf_chk
cmp ebx, 4
jnz short loc_804840A
; print carriage return character (CR)
mov dword ptr [esp], 0Ah ; c
add esi, 4
call _putchar
cmp esi, edi ; meet struct end?
jnz short loc_8048408 ; j=0
lea esp, [ebp-0Ch]
pop ebx
pop esi
pop edi
pop ebp
retn
main endp
1.24.4 Fields packing in structure.
One important thing is fields packing in structures^163.
Let’s take a simple example:
#include <stdio.h>
struct s
{
char a;
int b;
char c;
int d;
};
void f(struct s s)
{
printf ("a=%d; b=%d; c=%d; d=%d\n", s.a, s.b, s.c, s.d);
};
int main()
{
struct s tmp;
tmp.a=1;
tmp.b=2;
tmp.c=3;
tmp.d=4;
f(tmp);
};
As we see, we have twocharfields (each is exactly one byte) and two more —int(each — 4 bytes).
(^163) See also:Wikipedia: Data structure alignment