如何使用NASM查找字符串的长度? [英] How would I find the length of a string using NASM?

问题描述

我正在尝试使用NASM编写一个程序，该程序从命令行参数中获取输入.由于未提供字符串长度，因此我试图制作一个函数来计算自己的字符串.这是我的尝试，它使用指向ebx寄存器中的字符串的指针，并返回ecx中的字符串的长度:

I'm trying to make a program using NASM that takes input from command line arguments. Since string length is not provided, I'm trying to make a function to compute my own. Here is my attempt, which takes a pointer to a string in the ebx register, and returns the length of the string in ecx:

len:
    push ebx
    mov ecx,0
    dec ebx
    count:
        inc ecx
        inc ebx
        cmp ebx,0
        jnz count
    dec ecx
    pop ebx
    ret

我的方法是逐个字符地检查字符串，然后检查它是否为空.如果不是，我增加ecx并转到下一个字符.我相信问题是cmp ebx,0对于我正在尝试的操作是不正确的.如何正确检查字符是否为空?另外，还有其他我可以做得更好的事情吗?

My method is to go through the string, character by character, and check if it's null. If it's not, I increment ecx and go to the next character. I believe the problem is that cmp ebx,0 is incorrect for what I'm trying to do. How would I properly go about checking whether the character is null? Also, are there other things that I could be doing better?

推荐答案

您正在将ebx中的值与0进行比较，这不是您想要的. ebx中的值是内存中字符的地址，因此应像这样取消引用:

You are comparing the value in ebx with 0 which is not what you want. The value in ebx is the address of a character in memory so it should be dereferenced like this:

cmp byte[ebx], 0

此外，最后一个push ebx应该是pop ebx.

Also, the last push ebx should be pop ebx.

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