寻找新线路

Question

我是汇编新手，我的任务是读取文件名并打印该文件中的偶数行。我不知道如何找到一条新线。我知道我必须 cmp 13 和 10，因为那是马车 return，但我没有成功。任何帮助将不胜感激。这是我目前拥有的：

assume cs:code, ds:data
data segment
message1 db 'Name of the file: $'
message2 db 'Even linis: $'
maxFileName db 12
lFileName db ?
fileName db 12 dup (?)
buffer db 8 dup (?), '$'
openErrorMsg db 'Open error!$'
readErrorMsg db 'Read error!$'
data ends

code segment    
start:

    mov ax, data
    mov ds, ax

    ;print initial message
    mov ah, 09h
    mov dx, offset message1
    int 21h

    ;read name of the file
    mov ah, 0ah
    mov dx, offset maxFileName
    int 21h

    ;convert name of the file to ASCIIZ
    mov al, lFileName
    xor ah, ah
    mov si, ax
    mov fileName[si], 0

    ;open file
    mov ah, 3dh
    mov al, 0
    mov dx, offset fileName
    int 21h

    jc openError ;error <=> CF=1
    mov bx, ax

    ;end of line
    mov dl, 10
    mov ah, 02h
    int 21h
    mov dl, 13
    mov ah, 02h
    int 21h

    ;print second message
    mov ah, 09h
    mov dx, offset message2
    int 21h

    ;end of line
    mov dl, 10
    mov ah, 02h
    int 21h
    mov dl, 13
    mov ah, 02h
    int 21h

    read:
        mov ah, 3fh
        mov dx, offset buffer
        mov cx, 8 ;read 8 char
        int 21h
        jc readError ;error <=> CF=1

        cmp buffer, 0Dh
        je read

        ;save bytes number and add $ for printing
        mov si, ax
        mov buffer[si], '$'     

    afisare:
        ;print what have we read
        mov ah, 09h
        int 21h
        cmp si, 8
        je read ;if we read 8 bytes, we have yet to read all

    jmp endPb ;nu exista erori

    openError:
        mov ah, 09h
        mov dx, offset openErrorMsg
        int 21h
        jmp endPb

    readError:
        mov ah, 09h
        mov dx, offset readErrorMsg
        int 21h 

    endPb:
        mov ax,4c00h
        int 21h

    mov ax,4c00h
    int 21h
code ends
end start

Answer 1

问题出在您的 read 代码上。我添加了评论以使您更容易看出问题所在：

read:
    mov ah, 3fh              ; Read from file or device
    mov dx, offset buffer    ; Read destination
    mov cx, 8                ; Read 8 characters into buffer
    int 21h                  ; BIOS call
    jc readError             ; Check for error in carry flag

    ;;; vvv Here's your problem
    cmp buffer, 0Dh          ; Check to see if the memory address of
                             ; buffer is 0x0d
    ;;; ^^^ Here's your problem

    je read                  ; If the address is 0x0d, jump back and read again

如上所述，问题在于您将错误的东西与 0x0d 进行了比较。您可能打算这样做：

    cmp [buffer], 0dh

虽然这会比较数据而不是 buffer 的地址文字，但它仍然不完整。您真的想比较每个读取的 byte 以查看它是否包含 ASCII 13。我会把它留给您，因为这是家庭作业:)

寻找新线路

Finding a new line

assembly

dos

real-mode

16-bit