capture key problem

in c programming,
how can I capture keys like "page down", "ctrl+?", etc. using standard library?

You can't using the standard library. But you can use _kbhit() and _getch().

gg

I think that can't capture the 'page down',

any other method?

> I think that can't capture the 'page down',
Think again then

Extended keys arrive as two bytes - the first being zero

Code:

---

int mygetch ( void ) {
    int ch = getch();
    if ( ch == 0 ) ch = 256 + getch();
    return ch;
}

---

Now call this in a loop and print out the return value as you press each key, and study what is going on.

If you are coding in DOS you write and interrupt 9 handler. If it's in Windows you simply check for the correct VK code - after masking out the correct bits. Check the Windows SDK on that.

As for DOS (C++):

Code:

---


int keys[128];
#define Keydown(scan_code)  (if keys[scan_code]?1:0)
interrupt *OldHandler(...)=0;


int main(void)
{
  //Register atexit function
  atexit(UninstallHandler);
  ....
  ....
  return (0);
}

interrupt NewKeyHandler(...)
{
  int x=inportb(0x60);
  if (x>127)
  {
      keys[x - 127]=0;
  } else keys[x]=1;
}

void InstallHandler(void)
{
  getvect(0x09,OldHandler);
  setvect(0x09,NewKeyHandler);
}

void UninstallHandler(void)
{
  setvect(0x09,OldHandler);
}

---

thanks for all of you,

to Salem,
I know EXTENDED KEY needs two bytes,
I also find a link full of these extended keys,as below:
http://www.teletechnics.co.nz/refere...cii_codes.html

but, How can I capture them?

like:

Code:

---

char ch;
ch=getch();

if(ch=='????')
{
  do sth.
}

---

> I know EXTENDED KEY needs two bytes,
But your example code says that you don't

Read my code again - see how extended key codes get 256 added to them

So from your handy table

Code:

---

                59                3B        073        00111011        F1

---

You can write

Code:

---

int ch = mygetch( );
if ( ch == 256 + 59 ) {
    // F1 pressed
}

---

get ctrl and key E or left eg.

Code:

---

#include <windows.h>

// ... code

if( GetAsyncKeyState(VK_CONTROL) &&
    GetAsyncKeyState('E') )
{
    // do what ever
}

else if(GetAsyncKeyState(VK_LEFT) )
{
    // do what ever
}

---

unfortuately if you want to check if it's capital letters inputted, u must check for the shift or caps button.

all the virtual keys are here.
http://msdn.microsoft.com/library/de...alKeyCodes.asp

obviously this is only for windows :)

somewhere in there is

VK_PRIOR (21)
PAGE UP key

VK_NEXT (22)
PAGE DOWN key

also if ur using win NT/XP/2000 these work aswell

VK_LSHIFT Left-shift key.
VK_RSHIFT Right-shift key.
VK_LCONTROL Left-control key.
VK_RCONTROL Right-control key.
VK_LMENU Left-menu key.
VK_RMENU Right-menu key.

I am sorry to trouble you again, Salem

Your method is working well for keys F1--F12,
but the rest don't work.
what's wrong?

Code:

---

int mygetch ( void ) {
    int ch = getch();
    if ( ch == 0 ) ch = 256 + getch();
    return ch;
}

main()
{
  while(1)
  {
      if(mygetch()==256+81)  // 81 is PageDown
      break;
  }
}

---

Read the help on _getch(). Everything you needed to know is right there. Just have to read it.

Code:

---

int mygetch(void)
{
    int ch = getch();

    if (ch == 0)
    {
        ch = 256 + getch();
    }
    else if (ch == 0xE0)
    {
        ch = 512 + getch();
    }

    return ch;
}

---

gg

The Problem has been solved :)

thanks to all of you,
Special thanks to Salem and CodePlug.

to CodePlug and Salem,
I think plus 512 and 256 is not needed in the code anymore.

The Final Correct Code:

Code:

---

int mygetch(void)
{
    int ch = getch();

    if (ch == 0 || ch == 0xE0)
    {
        ch = getch();
    }
    return ch;
}


main()
{
  while(1)
  {
      if(mygetch()==81)  //81 is PageDown
      break;
  }
}

---

> if(mygetch()==81) //81 is PageDown
And how will you tell the difference if the user presses 'Q' instead?

Salem,
thank you for giving me such an inspirational hint.
I think I get it.
You mean 256 is necessary, right?
then the code must go this way:

Code:

---

int mygetch(void)
{
  int ch=getch();
  if(ch==0||ch==0xE0)
  {
      ch=256+getch();
  }
  return ch;
}

main()
{
  int ch=mygetch();
 
  switch(ch)
  {
  case 81:
      printf("you press 'Q' ");
      break;
  case 256+81:
      printf("you press 'page down' ");
      break;
  }
  getch();
}

---

-----------------------------------------------------------------

by the way,
I found that the arrow keys has no corresponding ASCII.
but I wrote some codes to try it, and found that they also has two-character , and the first is -32.
So I try to capture it the same way as above(simply replace 0 as -32).
It works all right.
Does it a correct way to capture arrow keys?
-------------------
how about the CTRL SHIFT and ALT ? I don't know how to try them.
-------------------
wish you can answer my boring questions altogether
:)
last,
what's this below? another way of capture keys?
#define SHIFT_R 0x0001
#define SHIFT_L 0x0002
#define CTRL 0x0004
#define ALT 0x0008
#define SCROLL_LOCK_ON 0x0010
#define NUM_LOCK_ON 0x0020
#define CAPS_LOCK_ON 0x0040


thank you so much.