Solved

how to write a loop to detect keyed input without stopping program

Posted on 2007-12-02
10
293 Views
Last Modified: 2011-10-03
What C++ code could I use to detect certain keypresses in a while loop. I want to write a calibration routine (simple : )) that will adjust offset other variables by a certain amount when I press right arrow, left arrow, up arrow and down arrow. I don't want the system to stop or pause for input; the other routines need to continue reunning. I am thinking of launching a thread to do this.

So how do I detect arrow keypresses....

0
Comment
Question by:Wanderinglazyeye
  • 3
  • 3
  • 2
  • +2
10 Comments
 
LVL 55

Expert Comment

by:Jaime Olivares
ID: 20392325
Which OS?
Which Envirnoment? console, window
Which Compiler?
Which compiler library?
0
 
LVL 11

Expert Comment

by:cup
ID: 20392340
Which OS are you using?  Different OSs generate different sequences for arrow keys.

If you're using windows, you could use _kbhit to detect whether the key had been pressed.  Saves having to launch a task.

On Unix, it is some ioctl sequence for the equivalent of windows _kbhit.

Don't know about other OSs.
0
 
LVL 86

Expert Comment

by:jkr
ID: 20392348
Use 'GetKeyState()' (http://msdn2.microsoft.com/en-us/library/ms646301.aspx), e.g.

int nState = GetKeyState('a');

if (0x80000000 & nState) {

  // 'a' is pressed
}

or 'GetKeyboardState() (http://msdn2.microsoft.com/en-us/library/ms646299.aspx)

BYTE keys[256];

GetKeyboardState(keys);

to get the whole keyboard state.
0
 
LVL 5

Expert Comment

by:abith
ID: 20393850
here is a small exp code which runs till pressing ESC key
for windows:
while(1)
{
   if (_kbhit())
   {
          c = _getch();
          if(c==27) // ESC
                 break;
    }
}

for unix
while(1)
{
    c = kb_getc()  ;
   if (c) // key is pressed
   {
         if(c==27)
           break;
   }
}
0
 
LVL 11

Expert Comment

by:cup
ID: 20397321
Source for kb_getc - this isn't a std unix call but the code is simple enough

unsigned char kb_getc(void)
{
    unsigned char ch;
    size_t size;

   size = read (STDIN_FILENO, &ch, 1);
   return size == 0? 0: ch;
}
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 11

Expert Comment

by:cup
ID: 20397357
Just a thought - it needs raw mode.  Might be better if you look at http://www.pwilson.net/kbhit.html for kb_getc if you're using unix.  It is pretty complex.
0
 

Author Comment

by:Wanderinglazyeye
ID: 20406600
No errors, but it doesn't detect the "a":


int i = 1;

	////////////////////////////////////////////////////////////////

	// Start Life Cycle

	////////////////////////////////////////////////////////////////

	while (i){

int nState = GetKeyState('a');

if (0x80000000 & nState) {

MessageBox(NULL,"A","Error",MB_OK);

  // 'a' is pressed

}

}

Open in new window

0
 
LVL 86

Accepted Solution

by:
jkr earned 500 total points
ID: 20406649
Try a capital 'A', the following works fine:

#include <windows.h>

void main () {

int i = 1;
        ////////////////////////////////////////////////////////////////
        // Start Life Cycle
        ////////////////////////////////////////////////////////////////
        while (i){
int nState = GetKeyState('A');
if (0x80000000 & nState) {
MessageBox(NULL,"A","Error",MB_OK);
  // 'a' is pressed
}
}
}
0
 

Author Comment

by:Wanderinglazyeye
ID: 20406918
What codes would I use for up arrow,right arrow, down arrow, left arrow, etc. More intelligently phrased, where can I find the map to codes I could select for keys from the keyboard?

Code works fine now.

WLE
0
 
LVL 86

Expert Comment

by:jkr
ID: 20407424
These are defined as VK_UP, VK_DOWN, VK_LEFT and VK_RIGHT. You will find all of them in winuser.h or in the table at http://www.codeproject.com/KB/system/keyboard.aspx
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Windows Script Host (WSH) has been part of Windows since Windows NT4. Windows Script Host provides architecture for building dynamic scripts that consist of a core object model, scripting hosts, and scripting engines. The key components of Window…
When we want to run, execute or repeat a statement multiple times, a loop is necessary. This article covers the two types of loops in Python: the while loop and the for loop.
This theoretical tutorial explains exceptions, reasons for exceptions, different categories of exception and exception hierarchy.
Viewers will learn how to properly install Eclipse with the necessary JDK, and will take a look at an introductory Java program. Download Eclipse installation zip file: Extract files from zip file: Download and install JDK 8: Open Eclipse and …

910 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now