difficult - Keyboard hook
Hi,
I need to do the following:
A barcode scanner is connected to the PS/2 input using a split cable (so, both the keyboard and the barcode scanner are connected to the same PS/2 port). The barcode scanner uses "keyboard simulation" to send it's code to the currently active application. If you open a texteditor and you scan a barcode, the number is send to the page.
You can add a "prefix" to the barcodescanner of maximum 10 keycodes or characters (like A, #, NULL,
etc...)
I want to use the barodescanner on the background, so I was planning to use a system wide keyboard hook which detects if there was a NULL-NULL send to the PS/2 input, and in this case takes the 13 following characters (I'm using EAN13 as barcode) and makes that they are send to a file, without that they are send to the active apllication (like MS Word, Outlook, ...).
Some extra information: The PC's on which it must work doesn't have either .NET1 or .NET2 .
I tried to make some demo code, but apparently this code won't work (because the NULL's aren't captured):
LRESULT __declspec(dllexport)__stdcall CALLBACK KeyboardProc(int nCode,WPARAM wParam,
LPARAM lParam)
{
char ch;
if (((DWORD)lParam &0x40000000) &&(HC_ACTION==nCode))
{
if ((wParam==VK_SPACE)||(wParam==VK_RETURN)||(wParam>=0x2f ) &&(wParam<=0x100))
{
f1=fopen("c:\\report.txt","a+");
if (wParam==VK_RETURN)
{
ch='\n';
fwrite(&ch,1,1,f1);
}
else
{
BYTE ks[256];
GetKeyboardState(ks);
WORD w;
UINT scan=0;
ToAscii(wParam,scan,ks,&w,0);
ch =char(w);
fwrite(&ch,1,1,f1);
}
fclose(f1);
}
}
LRESULT RetVal = CallNextHookEx( hkb, nCode, wParam, lParam );
return RetVal;
}
How should I adapt the code? Can someone give me some example code?
Thanks
[3829 byte] By [
plinius] at [2007-12-28]
Thanks a lot. I followed your advice.
I made some code using a
SetWindowsHookEx (WH_KEYBOARD_LL, LowLevelKeyboardProc ,...);
I filtered like that:
(wParam != WM_KEYDOWN)&& (wParam != WM_KEYUP)
which works fine.
I do have one more question though:
What I want to do now is, when it's a barcode which is scanned, it's not passed to the active application.
Therefore I putted this at the end of the callback function:
LRESULT RetVal=NULL;
if (!wasbarcode)
RetVal = CallNextHookEx(hKeyHook, nCode,wParam,lParam);
return RetVal;
But this doesn't seems to work?! I'm positively sure that the filter does what it should do.
(the only reason I could think of is the following:
I'm not working with a dll to hook but with a single exe (like this):
__declspec(dllexport) LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam ) {
bool wasbarcode=false;
What am I doing wrong ?
Should I work with a dll or is it something else I did wrong?
Thanks a lot !
I just tried that, and it doens't works .
It gave a very strange result:
every barcode was send to the application as before, exept all the 7's in the barcode were replaced by ?.
So, the code
8711875929908
Gave this in the "notepad-window":
8?118?5929908
I searched further but didn't found anything else...
Thanks.
OK. Found it. Now it works, but there's still one bug left:
whenever a barcode is scanned, the numpad doesn't works anymore...
Which is very annoying, because you have to unhook the application...
Here is the code (it's a bit ugly, should clean it up once...)
static bool wasbarcode=false;
static bool eerstevdtwee=true;
static int teller=0;
static int tempcijfer;
__declspec(dllexport) LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam ) {
bool laatstealtweg=false;
if ((nCode == HC_ACTION) ) {
if ((unsigned char)wParam == 0x05) {//hier dus: barcode gedeelte
wasbarcode=true;
teller++;
if(teller==26){wasbarcode=false;/*teller=0;*/}
printf("\nteller:%i\n",teller);
BYTE KeyState[256];
KBDLLHOOKSTRUCT hooked = *((KBDLLHOOKSTRUCT*)lParam);
GetKeyboardState(KeyState);
printf("\n--flags:%x--scancode:%x--vkcode:%x--tempcijf:%i",hooked.flags,hooked.scanCode,hooked.vkCode,(int)hooked.vkCode-96);
if(eerstevdtwee)
{tempcijfer=(int)hooked.vkCode-96;}
else{//dus tweede!
tempcijfer=(10*tempcijfer +((int)hooked.vkCode-96))-48;
printf("%i",tempcijfer);
}
eerstevdtwee=!eerstevdtwee;
}//eind barcodegedeelte
else{//hierin moet laatste ALT weggewerkt worden ! anders:?
if(teller==26){teller=0;laatstealtweg=true;}
}
}
return((wasbarcode || laatstealtweg) ? (LRESULT)1 : CallNextHookEx(hKeyHook, nCode,wParam,lParam));
}
