Finding a substring in a string and its position

Question

Guys im currently working on this small code in assembly to find a substring in a string using Assembly language , so my code here can find the substring , i need help to find the postion from where this substring starts

org 100h 

.data

buf1 DB "Enter String : $"

buf2 DB 0dh,0ah,"Enter Substring to search : $"

buf3 DB 0dh,0ah,"Substring Found $",1

buf4 DB 0dh,0ah,"Substring not Found...$"

str DB 120,120 DUP(?)

str_len DW 0

substr DB 120,120 DUP (?)

substr_len DW 0

counter DW 0   

.code

;initilize Data Segment

mov ax,@DATA

mov DS,ax

;==========Input String=====

lea dx,buf1

call Display

mov dx,offset str

mov ah,0Ah

int 21h

mov bl,[str+1]

mov str_len,bx

;=======Input Substring======

lea dx,buf2

call display

mov dx,offset substr

mov ah,0Ah

int 21h

;checking if substring is in string or not

lea SI,str ;SI contain String

add SI,2

lea DI,substr ;DI contain substring

add DI,2

mov bx,substr_len

cmp str_len,bx

jg G ;CX will contain greater value

mov cx,bx

G:

        mov cx,str_len
;======Cheking if substring or not====

L:

        lodsb
        cmp al,0Dh
        je final
        cmp al,' '
        jne next

final:

        cmp counter,0
        je exit
        mov counter,0
        lea DI,substr
        add DI,2
        jmp next1

next:

        dec SI

next1:

        cmpsb
        je h
        inc counter

h:

        LOOP L

exit:
        cmp counter,0
        je Found
        lea dx,buf4
        call Display
        jmp terminate

Found:

        lea dx,buf3
        call Display

terminate:

;to terminate program
        mov ah,4ch
        int 21h
        ret

Display PROC
mov ah,09h
int 21h
ret
Display ENDP

Does this answer your question? Finding the substring in an input string or Checking substring in 8086 asm. — U880D
– U880D, Commented Dec 10, 2020 at 16:38

Sep Roland · Accepted Answer · 2020-12-10 21:44:19Z

so my code here can find the substring

I find that very hard to believe! With so many errors it's a miracle that it even runs...

mov bl,[str+1]
mov str_len,bx

1 You only load a byte, but you write a word for which you did not clear the high half BH. Later you will be using the whole word.

mov bx,substr_len

2 You didn't even assign that substr_len variable from the input first.

  cmp str_len,bx
  jg G ;CX will contain greater value
  mov cx,bx
G:
  mov cx,str_len

3 If the inputted substring happens to be longer than the string, you need to abort because you can't hope to find a longer string inside a shorter string!

G:
  mov cx,str_len
  ;======Cheking if substring or not====

4 If anything, this CX loop counter should get loaded from the shortest string, which should be substr_len.

5 It's a mess. Please read this Q/A.

Please use the info from the link and come up with a better solution, especially one that is more readable. I am a gentle person :-) and will gladly take a look at your next effort. Don't hesitate to ask questions.

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