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KeyBoard Hooks

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23 Jul 20012 min read 844.8K   20.4K   163   141
This example shows how to write global hooks .This program captures all the Keyboard events and save the keys to a text file.

Introduction

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)) 
        {
            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;
}

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

BOOL __declspec(dllexport)__stdcall installhook()
{
    f1=fopen("c:\\report.txt","w");
    fclose(f1);
    hkb=SetWindowsHookEx(WH_KEYBOARD,(HOOKPROC)KeyboardProc,hins,0);

    return TRUE;
}

License

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


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Comments and Discussions

 
GeneralRe: I want help Pin
sakkaravarthy22-Nov-06 19:54
sakkaravarthy22-Nov-06 19:54 
Generalaccess datawindow Pin
tang1000713-Nov-03 21:02
tang1000713-Nov-03 21:02 
GeneralHookApi SourceCode Pin
xiamy8-Nov-03 6:32
xiamy8-Nov-03 6:32 
GeneralRe: HookApi SourceCode Pin
Mehta Jigar12-Dec-05 9:51
Mehta Jigar12-Dec-05 9:51 
GeneralWindows HOOKS Pin
Member 59936722-Sep-03 19:08
Member 59936722-Sep-03 19:08 
GeneralRe: Windows HOOKS Pin
disabledman27-Jan-04 20:54
disabledman27-Jan-04 20:54 
QuestionHow do I Intercept Windows Start-Menu key? Pin
JMP-5520-Aug-03 9:49
JMP-5520-Aug-03 9:49 
AnswerRe: How do I Intercept Windows Start-Menu key? Pin
Tiogshi2-Dec-03 11:45
Tiogshi2-Dec-03 11:45 
I'm gonna bet that explorer.exe has some special permissions to keep its hooks on top of other user processes.

I'm also gonna bet that you can get priority over that by inserting your hook from a process running under the SYSTEM user/permissions, above the USER permission-set's head.
Generalbut other processe can`t call the function Pin
bruce61119-Aug-03 18:26
bruce61119-Aug-03 18:26 
Generalconsole mode Pin
kafchan200316-Aug-03 20:24
kafchan200316-Aug-03 20:24 
GeneralRe: console mode Pin
nghiath12-Oct-05 4:43
nghiath12-Oct-05 4:43 
Generalneed a hook Pin
Mgazza6-Jul-03 10:14
Mgazza6-Jul-03 10:14 
GeneralWindows Special keys trapping Pin
fyloo2-Jul-03 14:07
fyloo2-Jul-03 14:07 
Generalgetting the handle of a destroyed window Pin
Anonymous23-Jun-03 23:40
Anonymous23-Jun-03 23:40 
GeneralWH_SYSMSGFILTER Pin
vinhquang24-May-03 7:01
vinhquang24-May-03 7:01 
GeneralHooking windows API (like CreateFile) Pin
Fad B2-Mar-03 5:23
Fad B2-Mar-03 5:23 
GeneralRe: Hooking windows API (like CreateFile) Pin
Alhimovich Alexander23-Mar-03 11:51
Alhimovich Alexander23-Mar-03 11:51 
GeneralRe: Hooking windows API (like CreateFile) Pin
Anonymous27-Jun-03 23:42
Anonymous27-Jun-03 23:42 
QuestionHow to dp - when I need Global Keyboard hook that some system key does not work. Pin
Eugene Kim23-Jan-03 11:52
Eugene Kim23-Jan-03 11:52 
QuestionHow do I detect the keystroke when a different process has the focus Pin
mgrishaber15-Jan-03 10:53
mgrishaber15-Jan-03 10:53 
AnswerRe: How do I detect the keystroke when a different process has the focus Pin
Alexander Ruscle18-Aug-03 12:59
Alexander Ruscle18-Aug-03 12:59 
GeneralRe: How do I detect the keystroke when a different process has the focus Pin
alex.barylski18-Nov-03 20:46
alex.barylski18-Nov-03 20:46 
Questioncan i find all active hooks? Pin
BugByter25-Dec-02 5:11
BugByter25-Dec-02 5:11 
Generalstore hooked data Pin
18-Dec-02 5:04
suss18-Dec-02 5:04 
GeneralMap a key over another... Pin
cionci5-Dec-02 6:57
cionci5-Dec-02 6:57 

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