I write a program to reverse a string it given, but it seems that the result didn't match.
I use foward and backward to indicate the index to exchange and finally add the null character in the tail.
The result should be
67 6E 69 72 74 73 20 65 63 72 75 6F 73 20 65 68 74 20 73 69 20 73 69 68 54 00
but My result is
00 67 6E 69 72 74 73 20 65 63 72 75 6F 73 20 65 68 74 20 73 69 20 73 69 68 00
it seem something wrong, bur I cannot find out where is the bug.
Could you help me to find where might be wrong?
Thx in advance.
INCLUDE Irvine32.inc
.data
source BYTE "This is the source string",0;26
target BYTE SIZEOF source DUP('#')
strl BYTE 0
foward DWORD 0
backward DWORD 0
.code
main PROC
mov strl, LENGTHOF source;26
dec strl; last char is 25. 26 is null
movzx ecx, strl;count = 25
mov foward, 0
movzx eax, strl
mov backward, eax
L1:
mov esi, backward
mov al,source[esi]
dec backward
mov esi, foward
mov target[esi], al
inc foward
loop L1
movzx esi, strl
mov al,source[esi]
mov target[esi], al
mov esi,OFFSET target ; offset of variable
mov ebx,1 ; byte format
mov ecx,SIZEOF target ; counter
call DumpMem
main ENDP
END main
Change this:
mov esi, backward
mov al,source[esi]
dec backward
To:
dec backward
mov esi, backward
mov al,source[esi]
because:
movzx eax, strl
mov backward, eax
initially backward points not to last element of string, but one after last (0 byte), so you first read it.