如何读取ascii字节字符串

Question

我正试图编写一个程序从输入读取字节字符串并以ascii格式存储它(字符串以0结束)。下面是我到目前为止的代码;在我读取字符串后，我不知道如何访问字符串中的最后一个字节并将其设置为0。

READ_ASCIIZ PROC
    PUSH BP
    MOV BP, SP
    MOV AH, 0AH
    MOV DX, 4H[BP]
    INT 21H
    POP BP
    RET 2H
READ_ASCIIZ ENDP

Answer 1

您可以用以下方式(使用nasm语法，未经测试):

  ; saved modified registers
  push  bx
  push  si
  ; get pointer to buffer
  mov   si, [bp+4]
  ; grab number of chars read 
  ; (zero-extending as the length is stored as a byte)
  movzx bx, byte [si+1]
  ; write zero at end of character buffer (overwriting the newline)
  ; (+2 since that's were the buffer starts)
  mov   byte [si+bx+2], 0
  ; restore registers
  pop   si
  pop   bx

(注意这不是最优化的方式)