我是汇编语言的新手,我有这个代码,假设要反转字符串长度,现在我知道我已经关闭,但程序因为某种原因不断崩溃。问题在于STRREV PROC。我在这段代码中做错了什么?
INCLUDE Irvine32.inc
.data
prompt BYTE "Enter String: ", 0
response BYTE 50 DUP(0)
message BYTE " Message entered. ",0
.code
swap MACRO a,b
xor a,b
xor b,a
xor a,b
endM
STRQRY PROC
push ebp
mov ebp, esp
push edx
push ecx
mov edx, [ebp+8]
call writestring
mov ecx, SIZEOF response
mov edx, OFFSET response
call readstring
pop ecx
pop edx
pop ebp
ret 4
STRQRY ENDP
STRLEN PROC
push ebp
mov ebp, esp
push ebx
push ecx
mov edx,[ebp+16]
mov eax, 0
counter:
mov cl,[edx+eax]
cmp cl, 0
JE done
inc eax
jmp counter
done:
pop ecx
pop ebx
pop ebp
ret 4
STRLEN ENDP
STRREV proc
push ebp
mov ebp, esp
push OFFSET response
call STRLEN
mov edx, [ebp+8]
mov esi, 0
dec eax
reverseloop:
mov ah, [edx+esi]
mov al, [edx+eax]
swap ah, al
mov [edx+esi],ah
mov [edx+eax],al
inc esi
dec eax
cmp esi, eax
jb reverseloop
ja finish
finish:
pop ebp
ret 4
STRREV endp
main PROC
push OFFSET prompt
call STRQRY
call writedec
mov edx,OFFSET message
call WriteString
push eax
call STRREV
mov edx, OFFSET response
call WriteString
exit
main ENDP
END main
答案 0 :(得分:1)
在你的函数的主要问题是改变AL和AH寄存器,然后用EAX的指针。
我决定根据你的代码写一个新的功能,使用正确的模拟器仔细阅读和调试代码。
STRREV proc
;opening the function
push ebp
mov ebp, esp
push OFFSET response
call STRLEN
mov edx, [ebp+8] ;edx = offset string to reverse
mov esi, 0
dec eax
mov ebx,edx ;ebx stores the pointer to the first character
add ebx,eax` ;now ebx store the pointer to the last character before the '$'
reverseloop:
mov ah, [edx] ;ah stores the value at string[loop count]
mov al, [ebx] ;al stores the value at string[len-loop count-1]
;"swap ah,al" is logiclly unnecessary
;better solution:
mov [ebx],ah ; string[loop count] = string[len-loop count-1]
mov [edx],al ; string[len-loop count-1] = string[loop count]
inc edx ;increment of the right-most pointer
dec ebx ;decrement of the right-most pointer
cmp ebx, eax ;compares the left-most pointer to the right-most
jb reverseloop
jmp finish ;"ja", there is no need to check a condition twice
finish:
pop ebp
ret 4
STRREV endp