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KeyBoard Hooks

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4.76 (39 votes)
23 Jul 2001
This example shows how to write global hooks .This program captures all the Keyboard events and save the keys to a text file.


Hooks are one of the most powerful features of Windows. We can hooks to trp all the events in the Windows environment. This example shows how to trap keyboard events and save the keys to a text file.

In the Microsoft® Windows™ operating system, a hook is a mechanism by which a function can intercept events (messages, mouse actions, keystrokes) before they reach an application. The function can act on events and, in some cases, modify or discard them. Functions that receive events are called filter functions and are classified according to the type of event they intercept. For example, a filter function might want to receive all keyboard or mouse events. For Windows to call a filter function, the filter function must be installed — that is, attached to a Windows hook (for example, to a keyboard hook). Attaching one or more filter functions to a hook is known as setting a hook. If a hook has more than one filter function attached, Windows maintains a chain of filter functions. The most recently installed function is at the beginning of the chain, and the least recently installed function is at the end.

When a hook has one or more filter functions attached and an event occurs that triggers the hook, Windows calls the first filter function in the filter function chain. This action is known as calling the hook. For example, if a filter function is attached to the Computer Based Training (CBT) hook and an event that triggers the hook occurs (for example, a window is about to be created), Windows calls the CBT hook by calling the first function in the filter function chain.

To maintain and access filter functions, applications use the SetWindowsHookEx and the UnhookWindowsHookEx functions.

An Example

The CALLBACK function in my example is given below..

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)) 
            if (wParam==VK_RETURN)
                   BYTE ks[256];

                WORD w;
                UINT scan=0;
                ch = char(w); 

    LRESULT RetVal = CallNextHookEx( hkb, nCode, wParam, lParam );
    return  RetVal;

The installhook function that is installing the hook function in my example is given below.

BOOL __declspec(dllexport)__stdcall installhook()

    return TRUE;


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

H. Joseph
United States United States
No Biography provided

Comments and Discussions

GeneralRe: Windows hook on Vista Pin
mywish1-Apr-10 22:34
Membermywish1-Apr-10 22:34 
AnswerRe: Windows hook on Vista Pin
AndrianG19-Nov-07 12:15
MemberAndrianG19-Nov-07 12:15 
QuestionUnHook Pin
Joe John17-Jul-06 19:19
MemberJoe John17-Jul-06 19:19 
AnswerRe: UnHook Pin
nico8017-Aug-06 19:43
Membernico8017-Aug-06 19:43 
GeneralCase Sensitivity and other problems Pin
Grey|Pixels5-Jul-06 3:28
MemberGrey|Pixels5-Jul-06 3:28 
GeneralChanging directory of report.txt Pin
Volarz31-May-06 15:35
MemberVolarz31-May-06 15:35 
Generaldoesn't work in terminal session Pin
benm9999999924-May-06 17:31
Memberbenm9999999924-May-06 17:31 
Generalblocking VK_ENTER using keyboard_hook Pin
ori kovacsi15-Apr-06 22:14
Memberori kovacsi15-Apr-06 22:14 
QuestionHide Dialog Pin
J51219822-Mar-06 19:43
MemberJ51219822-Mar-06 19:43 
QuestionSetWindowsHookEx:WINDOWS 2000 Pin
20-Oct-05 21:12
suss20-Oct-05 21:12 
AnswerRe: SetWindowsHookEx:WINDOWS 2000 Pin
J51219822-Mar-06 19:37
MemberJ51219822-Mar-06 19:37 
Questiontrap ALT+number Pin
Haridasi3-Sep-05 9:45
MemberHaridasi3-Sep-05 9:45 
GeneralMonitorize mouse global events in WINDOWS-CE; Pin
XBSANTOS3-May-05 22:34
MemberXBSANTOS3-May-05 22:34 
GeneralRe: Monitorize mouse global events in WINDOWS-CE; Pin
sakkaravarthy22-Nov-06 21:01
Membersakkaravarthy22-Nov-06 21:01 
GeneralRe: Monitorize mouse global events in WINDOWS-CE; Pin
Paul Heil27-Oct-10 5:33
MemberPaul Heil27-Oct-10 5:33 
GeneralGlobal Kyboard Hooks Pin
iontodirel1-Apr-05 23:08
Memberiontodirel1-Apr-05 23:08 
GeneralWH_KEYBOARD_LL not capture all key events Pin
XBSANTOS28-Mar-05 9:34
MemberXBSANTOS28-Mar-05 9:34 
GeneralWH_JOURNALRECORD Windows CE Global Hook is blocked! Pin
XBSANTOS24-Mar-05 7:33
MemberXBSANTOS24-Mar-05 7:33 
GeneralUnHook in VB Pin
Member 178485317-Mar-05 3:42
MemberMember 178485317-Mar-05 3:42 
GeneralGlobal Hooks for Pocket PC Pin
XBSANTOS11-Mar-05 7:11
MemberXBSANTOS11-Mar-05 7:11 
GeneralRe: Global Hooks for Pocket PC Pin
mavl42197-Sep-05 21:51
Membermavl42197-Sep-05 21:51 
Generalunhandled exception Pin
Member 17848537-Mar-05 5:41
MemberMember 17848537-Mar-05 5:41 
GeneralRe: unhandled exception Pin
Anonymous10-Mar-05 2:47
MemberAnonymous10-Mar-05 2:47 
GeneralRe: unhandled exception Pin
sakkaravarthy22-Nov-06 20:51
Membersakkaravarthy22-Nov-06 20:51 
Generaldifferentiate b/n virtual keys and Real Keyboard Event Pin
mahesh kumar s12-Oct-04 22:00
Membermahesh kumar s12-Oct-04 22:00 

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Posted 23 Jul 2001


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