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
The CALLBACK function in my example is given below..
LRESULT __declspec(dllexport)__stdcall CALLBACK KeyboardProc(int nCode,WPARAM wParam,
if (((DWORD)lParam & 0x40000000) &&(HC_ACTION==nCode))
if ((wParam==VK_SPACE)||(wParam==VK_RETURN)||(wParam>=0x2f ) &&(wParam<=0x100))
ch = char(w);
LRESULT RetVal = CallNextHookEx( hkb, nCode, wParam, lParam );
installhook function that is installing the hook function in my example
is given below.
BOOL __declspec(dllexport)__stdcall installhook()