typedef void *HHOOK;

typedef struct tagKBDLLHOOKSTRUCT {
    DWORD   vkCode;
    DWORD   scanCode;
    DWORD   flags;
    DWORD   time;
    ULONG_PTR dwExtraInfo;
} KBDLLHOOKSTRUCT, FAR *LPKBDLLHOOKSTRUCT, *PKBDLLHOOKSTRUCT;

KBDLLHOOKSTRUCT *pKbdStruct = (KBDLLHOOKSTRUCT*)lParam;
pKbdStruct->...

#define WH_KEYBOARD_LL     13
#define WH_MOUSE_LL        14
#define MB_ICONERROR			0x00000010L

typedef void *HHOOK;

typedef struct tagKBDLLHOOKSTRUCT {
    DWORD   vkCode;
    DWORD   scanCode;
    DWORD   flags;
    DWORD   time;
    long dwExtraInfo;
//    ULONG_PTR dwExtraInfo;
} KBDLLHOOKSTRUCT; //, FAR *LPKBDLLHOOKSTRUCT, *PKBDLLHOOKSTRUCT;

KBDLLHOOKSTRUCT *pKbdStruct;

// Callback function (called when a key is pressed) 
LRESULT __stdcall HookCallback(int nCode, WPARAM wParam, LPARAM lParam) {
    if (nCode >= 0) {
        // the action is valid: HC_ACTION.
        if (wParam == WM_KEYDOWN) {
            // lParam is the pointer to the struct containing the data needed, so cast and assign it to kdbStruct
            pKbdStruct = (KBDLLHOOKSTRUCT*)lParam;
//            kbdStruct = *((KBDLLHOOKSTRUCT*)lParam);
            // a key (non-system) is pressed.
            if (pKbdStruct.vkCode == VK_F1) {
                // F1 is pressed!
                MessageBox(NULL, "F1 is pressed!", "key pressed", MB_ICONINFORMATION);
            }
        }
    }

    // call the next hook in the hook chain. This is nessecary or your hook chain will break and the hook stops
    return CallNextHookEx(_hook, nCode, wParam, lParam);
}

void SetHook() {
    // Set the hook and set it to use the callback function above
    // WH_KEYBOARD_LL means it will set a low level keyboard hook. More information about it at MSDN.
    // The last 2 parameters are NULL, 0 because the callback function is in the same thread and window as the
    // function that sets and releases the hook. If you create a hack you will not need the callback function 
    // in another place then your own code file anyway. Read more about it at MSDN.
    if (!(_hook = SetWindowsHookEx(WH_KEYBOARD_LL, HookCallback, NULL, 0))) { 
        MessageBox(NULL, "Failed to install hook!", "Error", MB_ICONERROR);
    }

}

void ReleaseHook() {
    UnhookWindowsHookEx(_hook);
}


void init_startup () {
    // Set the hook
    SetHook();	
    on_close = ReleaseHook; 
    on_exit = ReleaseHook; 
}