MASM x86汇编字符串匹配程序故障求助：无法识别源字符串

核心问题：参数传递错误 #

你的Str_find过程通过栈接收源字符串和目标字符串的地址，但main中调用该过程前未将参数压入栈，导致过程中[ebp+8]和[ebp+12]取到的是栈内垃圾值，根本没有指向正确的字符串缓冲区，这是无法匹配的直接原因。

次要问题与优化点 #

1. main中残留无效代码enter code here，需删除。
2. 源字符串长度计算逻辑可以简化，避免指针来回偏移的混淆。
3. 未处理源字符串为空的边界情况（可选优化）。

修正后的完整代码 #

INCLUDE Irvine32.inc ; Include Irvine32 library for input/output functions

.data
sourceStr BYTE 100 DUP(0)   ; Buffer for source string
targetStr BYTE 100 DUP(0)   ; Buffer for target string

promptSource BYTE       "Enter source string (the string to search for): ", 0
promptTarget BYTE       "Enter target string (the string to search from): ", 0
promptContinue BYTE     "Do you want to do another search? y/n (all lower case): ", 0
errorMsg BYTE           "Invalid input. Please enter 'y' or 'n'.", 0dh, 0ah, 0
positionMsg BYTE        "Source string found at position ", 0
notFoundMsg BYTE        "Source string not found.", 0dh, 0ah, 0
continueChar BYTE 0         ; User input for continuation

.code
main PROC
    ; Clear the screen
    call Clrscr

    ; Prompt the user to enter the source string and read it
    mov edx, OFFSET promptSource
    call WriteString
    mov edx, OFFSET sourceStr
    mov ecx, SIZEOF sourceStr
    call ReadString
    call Crlf

    ; Prompt the user to enter the target string and read it
    mov edx, OFFSET promptTarget
    call WriteString
    mov edx, OFFSET targetStr
    mov ecx, SIZEOF targetStr
    call ReadString
    call Crlf

    ; Call the Str_find procedure to search for the source string in the target string
    push OFFSET targetStr      ; 压入目标字符串地址（对应Str_find的[ebp+12]）
    push OFFSET sourceStr      ; 压入源字符串地址（对应Str_find的[ebp+8]）
    call Str_find

    ; Check the result of the search and display appropriate message
    cmp eax, -1
    je NotFound
    mov edx, OFFSET positionMsg
    call WriteString
    call WriteDec
    call Crlf
    jmp ContinueSearch

NotFound:
    mov edx, OFFSET notFoundMsg
    call WriteString

ContinueSearch:
    ; Prompt the user if they want to do another search
    mov edx, OFFSET promptContinue
    call WriteString
    call ReadChar
    mov continueChar, al
    call Crlf

    ; Check user input for continuation and handle accordingly
    cmp al, 'y'
    je main
    cmp al, 'n'
    je ExitProgram
    mov edx, OFFSET errorMsg
    call WriteString
    jmp ContinueSearch

ExitProgram:
    ; Exit the program
    exit

main ENDP

; Str_find procedure
; Searches for the first occurrence of sourceStr in targetStr.
; Returns: EAX = position (0-based) if found, EAX = -1 if not found
Str_find PROC
    push ebp
    mov ebp, esp
    push edi
    push esi
    push ebx

    ; Initialize pointers to sourceStr and targetStr
    mov esi, [ebp+8]  ; 源字符串地址
    mov edi, [ebp+12] ; 目标字符串地址
    mov ebx, edi      ; 保存目标字符串起始位置，用于计算最终偏移

    ; 计算源字符串长度
    mov edx, 0
findLength:
    cmp BYTE PTR [esi], 0
    je lengthDone
    inc edx
    inc esi
    jmp findLength
lengthDone:
    ; 处理源字符串为空的边界情况：直接返回位置0
    cmp edx, 0
    je found

    ; 重置源字符串指针到起始位置
    mov esi, [ebp+8]

    ; Search for sourceStr in targetStr
searchLoop:
    mov ecx, edx          ; 加载源字符串长度到ECX，作为cmpsb的循环次数
    repe cmpsb            ; 逐字节比较，直到不匹配或ECX为0
    je found              ; 如果全部匹配，跳转到found分支

    ; 未匹配，移动目标指针到下一个字符，继续搜索
    inc ebx
    mov edi, ebx
    cmp BYTE PTR [edi], 0 ; 检查目标字符串是否已到末尾
    jne searchLoop        ; 未到末尾则继续循环

notFound:
    ; Set EAX to -1 to indicate source string not found
    mov eax, -1
    jmp finish

found:
    ; Calculate the position of the source string in the target string and store it in EAX
    sub ebx, [ebp+12]     ; 用当前起始位置减去目标字符串基地址，得到0-based偏移
    mov eax, ebx

finish:
    ; Clean up the stack and return
    pop ebx
    pop esi
    pop edi
    pop ebp
    ret 8                 ; 清理栈上的两个双字参数（共8字节）
Str_find ENDP

END main

关键修正说明 #

1. 参数传递：调用Str_find前先压入目标字符串地址，再压入源字符串地址，与过程中[ebp+12]（目标）、[ebp+8]（源）的取值逻辑对应。
2. 长度计算：改为从源字符串起始位置逐字节计数，逻辑更直观，避免原代码中指针来回偏移的错误风险。
3. 边界处理：新增源字符串为空时直接返回位置0的逻辑，完善鲁棒性。

内容的提问来源于stack exchange，提问作者Nicholas