How to hook & remap keys

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Hello, I am working on my end-of-college project and I need to make a DLL to hook and remap some keyboard keys before they are send to the focused program. Example: my program runs in back and when I press A in notepad to write B.

I hope someone can help me :D
Thank you very much, Daniel!

Posted 16-May-10 11:33am

xspitfirexx

Updated 16-May-10 12:49pm

Moak

v2

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Solution 2

Hello everybody I have too same problem. I'm going to finish my bachelor work and i have to track the registry key work then used to use same logic in Process of OS.

Please somebody help me to get this type of code for my project. I have a few time. To think and finish it. You will be thankful for this job. Actually it's being difficult to find all of change in process of OS. But i have to get it and compare the result with timeinterval result.

Posted 17-May-10 9:47am

mcsqure

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Sauro Viti · Accepted Answer · 2010-05-17T07:05:00

Solution 1

Try have a look to this page and the related resources, from the MSDN library:

http://msdn.microsoft.com/en-us/library/ms644990(VS.85).aspx[^]

I think that what you need as first step is a low-level keyboard hook (see WH_KEYBOARD_LL) to process keys before that they are dispatched to the active application.

Note that from the installed hook procedure you have only two choices:

avoid further processing on the sent key

call the next installed hook (this means that your application does nothing on the sent key, and if no more hooks are installed the sent key is dispatched to the active application)

Then to remap some keyboard keys what you should do is something like the following:

install your hook procedure

from your hook procedure identify the keyboard keys that shouldn't be remapped and let them be processed by calling CallNextHookEx

avoid processing of keyboard keys that should be remapped and send a WM_CHAR message with the remapped key code to the active application

Posted 17-May-10 7:05am

Sauro Viti

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doanwon 10-Jun-10 0:31am

I tried the hook procedure and post a message to the hook handler. But the KBDLLHOOKSTRUCT that is supposed to be passed via LPARAM cannot be accessed. How would I get to this struct in your hook handler? The LPARAM is supposed to contain the struct info but I sizeof(l) = 4 so there is not much info. Casting l to a defined struct did not work. Would appreciate answer. Thanks.

Sauro Viti 10-Jun-10 2:17am

Via LPARAM is passed not the struct, but a pointer to the struct

doanwon 10-Jun-10 7:42am

No, I casted lparam to KBDLLSTRUCT pointer inside the hook handler but it returned garbage. However, casting the lparam inside the dll did work and I was able to access the vkCode to pass as the lparam or wParam (ULONG both). However, I cannot stop the program from processing the input key instead of letting my hook handler do perform this task. I tried PeekMessage to remove the message from queue but the program crashes--perhaps the message has not been placed onto queue.

I am using the Keyexe and Keydll program. The Keydll is compiled under VS2008 and Keyexe under VC++6 because I've added some stuff and was not able to compile under 2008--perhaps this is the problem. I am resorting use WH_CALLWNDPROC but I dont have a clue how to check what's in the struct (lparam). Everything I've tried crashed. With all due respect, Sauro, you are just reading the library and explaining to us--you have not tried to run the program. But I appreciate any recommendation.

Sauro Viti 10-Jun-10 9:42am

// This install the hook procedure (I suppose you are calling it from an MFC exe application)
hHook = SetWindowsHookEx(WH_KEYBOARD_LL, &LowLevelKeyboardProc, theApp.m_hInstance, 0);

// This is my hook procedure (it uses the KBDLLHOOKSTRUCT and it works properly...)
LRESULT CALLBACK LowLevelKeyboardProc(INT iCode, WPARAM wParam, LPARAM lParam)
{
if (iCode == HC_ACTION) {
KBDLLHOOKSTRUCT* pkbhs = (KBDLLHOOKSTRUCT *)lParam;
BOOL bCtrl = GetAsyncKeyState(VK_CONTROL) >> (8 * sizeof(SHORT) - 1);
BOOL bShift = GetAsyncKeyState(VK_SHIFT) >> (8 * sizeof(SHORT) - 1);

if (pkbhs->vkCode == VK_ESCAPE && pkbhs->flags & LLKHF_ALTDOWN) return 1;
else if (pkbhs->vkCode == VK_TAB && pkbhs->flags & LLKHF_ALTDOWN) return 1;
else if (pkbhs->vkCode == VK_ESCAPE && bCtrl) return 1;
else if (pkbhs->vkCode == VK_LWIN) return 1;
else if (pkbhs->vkCode == VK_RWIN) return 1;
else if (pkbhs->vkCode>=VK_BROWSER_BACK && pkbhs->vkCode<=VK_LAUNCH_APP2) return 1;
}

return CallNextHookEx(hHook, iCode, wParam, lParam);
}

doanwon 10-Jun-10 12:27pm

Thanks for taking the time. This is similar to what I have been trying, but the foreground app still processed all the incomming keystrokes. I added:
else if (pkbhs->vkCode == 41) return 1; //A
else if (pkbhs->vkCode == 31) return 1; //1
and WordPad still printed those chars out.

VC++6 did not recognize the WH_KEYBOARD_LL flag. But the above code is all in the DLL, which was compiled by VS2008 so it should not have mattered. Someone should report this to MS. I will have to resort to PeekMessage--even this does not work will KEYBOARD_LL.

Thanks again for your time.

Sauro Viti 10-Jun-10 15:23pm

I think that there is something wrong!Have a look to the page I posted about SetWindowsHookEx, on the Remarks section about LowLevelKeyboardProc callback, they says:

"This hook is called in the context of the thread that installed it. The call is made by sending a message to the thread that installed the hook. Therefore, the thread that installed the hook must have a message loop."

So, to work properly, the hook procedure must have been installed by a thread that handle a message loop, if your application is an MFC application the best place to put the call to SetWindowsHookEx is the constructor of your main window class. Note that worker threads and console applications do not have a message loop.

Just a style hint... why don't you write:

else if (pkbhs->vkCode == 'A') return 1;

instead than:

else if (pkbhs->vkCode == 41) return 1; // A

doanwon 10-Jun-10 17:22pm

Sorry Sauro, but you are getting a little condescending. FYI, an 'A' is 65 not 41--the virtual key is not the same as char value! Don't give hints unless you know what you are talking about. I have worked on this and other char for a long time so I deliberately used the number 41 instead of the char.

Back to this problem... I mentioned I used Keyexe and Keydll, which is a codeproject program--perhaps you can search for it. But you have not done any keymapping program and dispensing your advice... Well, I appreciate your time in trying to help others. Over and out!

doanwon 10-Jun-10 18:15pm

My mistake... 41 hex is 65 dec

Sauro Viti 10-Jun-10 18:54pm

No problem! I hope it works properly now... had you wrote 41 instead than 0x41?

doanwon 10-Jun-10 19:09pm

My apologies, Sauro. It works now! Thank you.

Sauro Viti 10-Jun-10 20:01pm

very well! so good luck for your end-of-college exam!