当我按键盘上的键时如何防止重复的字符 [英] How to prevent duplicate chars when I press keys on the keyboard
问题描述
我正在尝试学习如何防止键盘在DOS下向屏幕和scanf发送多个字符.我正在将Turbo-C与内联汇编一起使用.
I am trying to learn how to prevent the keyboard sending multiple chars to the screen and to scanf under DOS. I am using Turbo-C with inline assembly.
如果在键盘上输入的字符是:
If the characters entered on the keyboard are:
mmmmmmmmyyyyy nnnnnaaaaammmmmmeeeeeeee iiiiiissss HHHHaaaaiiiimmmm
mmmmmmmmyyyyy nnnnnaaaaammmmmmeeeeee iiiiiissss HHHHaaaaiiiimmmm
在控制台上看到并由scanf处理的字符为:
The characters seen on the console and processed by scanf would be:
我叫Haim
my name is Haim
基本输出来自 C 中的代码，我无法触摸.我必须实现eliminate_multiple_press和uneliminate_multiple_press而不接触它们之间的代码.
The basic output comes from the code in C which I am not allowed to touch. I must implement eliminate_multiple_press and uneliminate_multiple_presswithout touching the code in between.
到目前为止，我编写的Turbo-C代码是:
The Turbo-C code I've written so far is:
#include <stdio.h>
#include <dos.h>
#include <string.h>
volatile char key;
volatile int i=0;
void interrupt (*Int9save) (void);
void interrupt kill_multiple_press()
{
asm{
MOV AL, 0
MOV AH,1
INT 16h
PUSHF
CALL DWORD PTR Int9save
MOV AX,0
}
asm{
JZ notSet
MOV key, AL
MOV AH, 04H
INT 16H
}
notSet:
//I am not sure what to do from here...............
I also know that it should be related to the zero flag, but what I
wrote so far didn`t effect on multiple characters.
}
void eliminate_multiple_press()
{
Int9save=getvect(9);
setvect(9,kill_multiple_press);
}
void uneliminate_multiple_press()
{
setvect(9,Int9save);
}
void main()
{
char str[10000]="";
clrscr();
eliminate_multiple_press();
printf("Enter your string: ");
scanf("%s",&str);
printf("\n%s",str);
uneliminate_multiple_press();
}
我得到的与解决方案有关的信息是可以在此找到的键盘BIOS例程.链接:
Information I have been given that relate to a solution are the keyboard BIOS routines that can be found at this link:
我遇到的问题可能与不了解标签notSet的操作有关.该解决方案似乎与使用缓冲区和寄存器 AX (尤其是 AL )有关，但是我真的不知道如何制作scanf以获得结果需要.有谁知道如何完成此代码以达到预期的效果?
The problems I'm having are probably related to not understanding what to do at the label notSet. The solution seems to be related to using a buffer and the register AX (especially AL), but I really have no Idea how to make scanf to get the result I need. Does anyone have any ideas how I can complete this code to achieve the desired effect?
推荐答案
BIOS，DOS和 C 库(包括scanf)可能使用多层缓冲区.当计算机启动时，中断向量表被修改为将IRQ1/ INT 9h (外部键盘中断)指向BIOS例程，以处理键入的字符.在最低级别，通常有32个字节 6 圆形缓冲区在 BIOS数据区域(BDA)中进行维护以跟踪字符.您可以使用 Int 16h BIOS调用 1 与该低级键盘缓冲区进行交互.如果在中断时从BIOS键盘缓冲区中删除字符，则DOS和 C 库scanf 5 例程将永远看不到它们.
There are multiple layers of buffers that may be used by the BIOS, DOS, and the C library (including scanf). When your machine starts up the interrupt vector table is modified to point IRQ1/INT 9h (the external keyboard interrupt) to a BIOS routine to handle characters as they are typed. At the lowest level there is usually a 32 byte6 circular buffer that is maintained in the BIOS Data Area (BDA) to keep track of the characters. You can use the Int 16h BIOS calls1 to interact with this low level keyboard buffer. If you remove characters from the BIOS keyboard buffer at interrupt time then DOS and the C library scanf5 routine will never see them.
在BIOS/中断级别消除重复字符的方法
看来，练习是通过通过中断9(IRQ1)拦截击键并丢弃重复项来消除输入到scanf 3 中的所有重复的 2 字符.一种新的键盘中断处理程序的想法是在DOS(并最终成为scanf)看到重复项之前消除重复项:
It appears that the exercise is to eliminate all duplicate2 characters entered into scanf3 by intercepting keystrokes via Interrupt 9 (IRQ1) and throwing duplicates away. One idea for a new keyboard interrupt handler to eliminate the duplicates before DOS (and eventually scanf) ever see them:
- 跟踪变量中按下的前一个字符
- 调用原始的(保存的)中断9，以便BIOS根据DOS的要求更新键盘缓冲区和键盘标志.
- 通过 Int 16h/AH = 1h查询键盘上的字符是否可用.如果没有可用字符，则将设置零标记(ZF)，如果有可用字符，则将其清除.此键盘BIOS调用会窥视键盘缓冲区的开始，而不会实际删除下一个可用字符.
- 如果有可用字符，则将其与上一个字符进行比较.
- 如果它们不同，则使用当前字符更新前一个字符并退出
- 如果它们相同，则使用整数16h/AH = 0h 从键盘缓冲区中删除重复的字符并退出
- Keep track of the previous character pressed in a variable
- Call the original (saved) Interrupt 9 so that the BIOS updates the keyboard buffer and the keyboard flags as DOS expects them to appear.
- Query the keyboard to see if a character is available with Int 16h/AH=1h.The Zero Flag (ZF) will be set if no characters are available and clear if there is one available. This keyboard BIOS call peeks into the beginning of the keyboard buffer without actually removing the next character available.
- If a character is available then compare it with the previous character.
- If they are different then update the previous character with the current character and exit
- If they are the same then use Int 16h/AH=0h to remove the duplicate character from the keyboard buffer and exit
Turbo-C 3.0x版本的代码 4 :
A Turbo-C 3.0x version of the code4:
#include <stdio.h> #include <dos.h> #include <string.h> #include <conio.h> volatile char key = 0; void interrupt (*Int9save)(void); void interrupt kill_multiple_press(void) { asm { PUSHF CALL DWORD PTR Int9save /* Fake an interrupt call to original handler */ MOV AH, 1 /* Peek at next key in buffer without removing it */ INT 16h JZ noKey /* If no keystroke then we are finished */ /* If ZF=1 then no key */ CMP AL, [key] /* Compare key to previous key */ JNE updChar /* If characters are not same, update */ /* last character and finish */ /* Last character and current character are same (duplicate) * Read keystroke from keyboard buffer and throw it away (ignore it) * When it is thrown away DOS and eventually `scanf` will never see it */ XOR AH, AH /* AH = 0, Read keystroke BIOS Call */ INT 16h /* Read keystroke that has been identified as a */ /* duplicate in keyboard buffer and throw away */ JMP noKey /* We are finished */ } updChar: asm { MOV [key], AL /* Update last character pressed */ } noKey: /* We are finished */ } void eliminate_multiple_press() { Int9save = getvect(9); setvect(9, kill_multiple_press); } void uneliminate_multiple_press() { setvect(9, Int9save); } void main() { char str[1000]; clrscr(); eliminate_multiple_press(); printf("Enter your string: "); /* Get a string terminated by a newline. Max 999 chars + newline */ scanf("%999[^\n]s", &str); printf("\n%s", str); uneliminate_multiple_press(); }
注释
- 1 在键盘中断处理程序内，您要避免任何会 block 等待键盘输入的键盘BIOS调用.如果使用 Int 16h/AH = 0 ，请确保首先有一个可用字符，而 Int 16h/AH = 1 否则为 Int 16h/AH = 0 >会在等待另一个角色到达时阻塞.
- 2 删除重复字符与禁用键盘重复率不同.
- 3 因为在DOS例程看到重复项之前它们已经被删除(以及依赖于DOS的
scanf之类的功能)，所以scanf将永远不会看到它们. - 4 可能需要进行一些修改才能与3.0x以外的Turbo-C版本兼容.
- 5 此方法仅适用于因为
scanf将间接进行BIOS调用，使键盘缓冲区保持畅通.此代码不适用于所有通用情况，尤其是在BIOS可能会缓冲击键的情况下.要解决这个问题，键盘中断例程将必须删除所有，而不是像此代码一样直接删除键盘缓冲区中的重复项. - 6 每个击键占用BIOS键盘缓冲区(在 BDA 中)的2个字节的空间. 32个字节中的2个丢失，因为它们用于检测键盘缓冲区是满还是空.这意味着BIOS可以缓冲的最大击键次数为15.
- 1Within the keyboard interrupt handler you want to avoid any keyboard BIOS call that will block waiting for keyboard input. If using Int 16h/AH=0 make sure there is a character available first with Int 16h/AH=1 otherwise Int 16h/AH=0 will block while waiting for another character to arrive.
- 2Removing duplicate characters is not the same as disabling the keyboard repeat rate.
- 3Because the duplicates are removed before DOS routines see them (and functions like
scanfthat rely on DOS), they will never be seen byscanf. - 4Some modifications may have to be made to be compatible with versions of Turbo-C other than 3.0x.
- 5This method only works because
scanfwill be indirectly making BIOS calls keeping the keyboard buffer clear. This code does't work in all generic cases especially where keystrokes may be buffered by the BIOS. To get around that the keyboard interrupt routine would have to remove all the duplicates in the keyboard buffer not just at the head as this code does. - 6Each keystroke takes up 2 bytes of space in the BIOS keyboard buffer (in the BDA). 2 of the 32 bytes are lost because they are used to detect if the keyboard buffer is full or empty. This means the maximum number of keystrokes the BIOS can buffer is 15.
Notes
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