cmp help

Any ideas why this wont work? Im compilng with A86.

START:
        mov     ds, cs
        jmp     MAIN

Message1        db      13, 10, "Password    [pass.exe]", 13, 10
                db      "Copyright (C) 2000 Hero Inc. All rights reserved.", 13, 10, "$"
Prompt          db      13, 10, "Password: $"
Password        db      "hello$"
Buffer          db      "$"

MAIN:
        ;Clear
        call    ClearScreen

        ;Print Message1
        mov     dx, offset Message1
        mov     ah, 9
        int     21h

        ;Print Prompt
        mov     dx, offset Prompt
        mov     ah, 9
        int     21h

        ;Input string
        mov     ah, 3fh
        xor     bx, bx
        mov     cx, 20h
        mov     dx, offset Buffer
        int     21h

        mov     ax, offset Buffer
        cmp     ax, offset Password

        je      EXIT
        jmp     MAIN

EXIT:
        call    ClearScreen
        mov     ax, 4c00h
        int     21h

ClearScreen     proc
        mov     ax, 0003h
        int     10h
        ret
ClearScreen     endp

END START

I think it has something to do with these lines...

mov     ax, offset Buffer
cmp     ax, offset Password

[Sam Finch]

I think it's a bit ambitious to try to compare 2 strings with a single cmp line. all cmp does is subtract the 2 values and save the reruld to a register (can't remember which one, i think it's dx or it might be a special 2 bit register that just rempmbers the sign) then the jump commands go on whether this it +ve, -ve or 0.

I havn't got to the offset comand in my quest to learn ASM but i think you're just comparing the pointers to the strings, which will never be equal. either write a strcmp macro or a strcmp sub.

hope it helps

Any code ideas?

[Sam Finch]

err, you want pointers to the 2 strings in 2 registers say ebx and ecx then go into a loop, compare the values of the 2 bytes pointed to by ebx and ecx if they are not equal put a value of 0 (false) into eax, if they are equal check if one of them is 0, if it is put -1 (true) into eax and return, if not increment ebx and eax and go back to the start of the loop.

Unfortunatley I'm not quite at the stage where I can code that correctly, so I'll code it incorectly instead

StringCompare proc

    pop ebx    ;pops 2 parameters off the stack, 
    pop ecx    ;these should be pointers to char arrays 

strt:    ;start of loop

        cmp [ebx],[ecx]  ;compare the bytes pointed to by
                         ;ebx and ecx, this syntax is
                         ;probably vey wrong so change it
                         ;remember you only want to compare 
                         ;single bytes, not words or dwords

        jne RetFalse  ;if they are not the same return false

        cmp [ebx], 0    ;compare the byte pointed to by ebx
                        ;to 0 (syntax will be wrong again)

jne strt        ;if it's not a termination character 
                ;go back to the start

;end of loop

;both strings terminated so return true
mov eax, -1
ret


RetFalse:
;we've found 2 different characters so return false   
    mov eax, 0
    ret

StringCompare endp

if you code that correctly it should work.

[V(ery) Basic]

I was just wondering, maybe if you XOR them then the first value in the XOR would be zero, and then put a jz.

But that wouldn't be case sensitive, so you could convert it to lower case by anding each char with 6F (0110 1111).

Okay, I'm probably speaking rubbish, but the intention's good.

[Darkwraith]

mov ax, BYTE [Buffer]
cmp ax, BYTE [Password]

I am not very good with A86, so I might be a little off. I am using the NASM syntax though

If you are comparing the values at Buffer and Password, then this would be your code.