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

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....

WanderinglazyeyeAsked:
Who is Participating?
 
jkrConnect With a Mentor Commented:
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
 
Jaime OlivaresSoftware ArchitectCommented:
Which OS?
Which Envirnoment? console, window
Which Compiler?
Which compiler library?
0
 
cupCommented:
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
Cloud Class® Course: SQL Server Core 2016

This course will introduce you to SQL Server Core 2016, as well as teach you about SSMS, data tools, installation, server configuration, using Management Studio, and writing and executing queries.

 
jkrCommented:
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
 
abithCommented:
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
 
cupCommented:
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
 
cupCommented:
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
 
WanderinglazyeyeAuthor Commented:
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
 
WanderinglazyeyeAuthor Commented:
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
 
jkrCommented:
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
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.