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请帮忙看看这个小程序# Programming - 葵花宝典

s*l2010-04-01 07:04

1 楼

Describe what happens in the following code:
short old;
short *ptr= (short *)0xB80000;
old = *ptr++; // What happens here
*ptr = (old<<1); // What happens here and what is ptr pointing to?

z*e2010-04-01 07:04

2 楼

deference at arbitrary memory location?
where is 0xB80000?

X*r2010-04-01 07:04

3 楼

Text mode video memory mapped under x86 real mode, if I recall correctly.
So this code, under DOS, would read the left-most character
of the first line on the screen, mutate it, and put the result
back on the next position.

【在 z****e 的大作中提到】

: deference at arbitrary memory location?
: where is 0xB80000?

z*e2010-04-01 07:04

4 楼

我靠，红猪侠你是干什么的？黑客？

【在 X****r 的大作中提到】

: Text mode video memory mapped under x86 real mode, if I recall correctly.
: So this code, under DOS, would read the left-most character
: of the first line on the screen, mutate it, and put the result
: back on the next position.

t*t2010-04-01 07:04

5 楼

B80000 > 1M so that's definitely unrelated to DOS...

【在 X****r 的大作中提到】

X*r2010-04-01 07:04

6 楼

Err... right, I counted 0s wrong.
Under DOS the video memory address would be B800:0000,
which is 0xB8000, but presented as 0xB8000000 in far pointers.

【在 t****t 的大作中提到】

: B80000 > 1M so that's definitely unrelated to DOS...