"13，10"代表什么?在"DB 13，10，'hello world'，0"中表示什么? [英] What does "13, 10" mean in "DB 13, 10, 'hello world', 0"?

问题描述

很长一段时间以来我一直在键入DB 13, 10, 'hello world', 0，却不知道13、10和0代表什么.

I've been typing DB 13, 10, 'hello world', 0 for a long time without wondering what the 13, the 10 and the 0 were for.

我最近注意到这样做:

PTHIS
DB 'hello world', 0

产生了相同的结果，所以我想知道第一个参数是什么意思，以这种方式简单地编写它是否是一个好主意.有人可以对此写一个简短的解释吗? (我想字符串声明将是主题)

produced the same result, so I'm wondering what the first parameters are for and whether is a good idea to simply write it this way. Could someone write a quick explanation on this? (I suppose string declarations would be the topic)

推荐答案

这是ASCII CR/LF(回车/换行)序列，用于前进到下一行的开头.

It's the ASCII CR/LF (carriage return/line feed) sequence, used for advancing to the beginning of the next line.

历史课:在旧的电传打字机上，回车确实做到了这一点，它将回车(打印头)返回到当前行的开头，同时换行使纸张前进，以便打印发生在下一行.

History lesson: On old teletype machines, carriage return did exactly that, it returned the carriage (printing head) to the start of the current line, while line feed advance the paper so that printing would happen on the next line.

您的两个样本不应产生相同的结果.如果在输出不带CR/LF的字符串时光标不在行首，则Hello world将显示在某行的中间行，即使您 do 从该行的开头开始一行，带有CR/LF的版本应首先将光标向下移动一行.

And your two samples shouldn't produce the same result. If your cursor is not at the start of a line when you output the string without CR/LF, the Hello world will show up mid-line somewhere and, even if you do start at the start of a line, the version with CR/LF should first move the cursor down one row.

最后的零只是字符串的终止符.一些早期的系统在原始BIOS中使用了其他字符，例如$:

The zero at the end is simply a terminator for the string. Some early systems used other characters like the $ in the original BIOS:

str   db "Hello, world$"

这使得将$符号输出到控制台相当麻烦:-)

which made it rather a pain to output the $ sign to the console :-)

之所以有终止符，是因为您的字符串输出几乎可以肯定是根据字符输出来编写的，例如伪asm代码:

The terminator is there because your string output will almost certainly be written in terms of a character output, such as the pseudo-asm-code:

; func:   out_str
; input:  r1 = address of nul-terminated string
; uses:   out_chr
; reguse: r1, r2 (all restored on exit)
; notes:  none

out_str   push    r1            ; save registers
          push    r2

          push    r1            ; get address to r2 (need r1 for out_chr)
          pop     r2

loop:     ld      r1, (r2)      ; get char, finish if nul
          cmp     r2, 0
          jeq     done

          call    out_chr       ; output char, advance to next, loop back
          incr    r2
          jmp     loop

done:     pop     r2            ; restore registers and return
          pop     r1
          ret

; func:   out_chr
; input:  r1 = character to output
; uses:   nothing
; reguse: none
; notes:  correctly handles control characters

out_chr   ; insert function here to output r1 to screen

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