Click here to Skip to main content
Click here to Skip to main content

KeyBoard Hooks

, 23 Jul 2001
Rate this:
Please Sign up or sign in to vote.
This example shows how to write global hooks .This program captures all the Keyboard events and save the keys to a text file.
<!-- Download Links --> <!-- Main HTML starts here -->

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

Share

About the Author

H. Joseph

United States United States
No Biography provided

Comments and Discussions

 
QuestionHow to set Key combination (like SHIFT+F9 etc.) as hook PinmemberMember 783682923-Aug-11 19:57 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Mobile
Web03 | 2.8.140827.1 | Last Updated 24 Jul 2001
Article Copyright 2001 by H. Joseph
Everything else Copyright © CodeProject, 1999-2014
Terms of Service
Layout: fixed | fluid