How to add a hook to Keyboard (HookProc) - c++

Question

I was trying to make a simple keylog test, but my program doesn't work as expected and I don't know why.
In my program i had a low level keyboard hook and attach a simple process to it. The process just opens/creates a file and writes "Hello World" then closes. However it isn't creating the file, probably because my process isn't correct or because my hook wasn't established correctly.
Code:
#include<windows.h>
#include<stdio.h>
#include <iostream>
#include <fstream>
using namespace std;
LRESULT CALLBACK KeyboardProc(int code, WPARAM wParam, LPARAM lParam){
ofstream myfile;
myfile.open ("[PATH]/example.txt");
myfile << "Hello world";//((KBDLLHOOKSTRUCT *)lParam)->vkCode
myfile.close();
return CallNextHookEx(NULL,code,wParam,lParam);
}
int main(void){
HINSTANCE hInst = NULL;
HHOOK hHook = SetWindowsHookEx(WH_KEYBOARD_LL, KeyboardProc, hInst, 0);
printf("HHOOK is not null: %s\n", (hHook != NULL) ? "True" : "False");
char q;
for (cout << "q to quit\n"; q != 'q'; cin >> q);
printf("Successfully unhooked: %s", UnhookWindowsHookEx(hHook) ? "True" : "False");
}
Solution I needed to add a message loop to the main function:
LPMSG Msg;
while(GetMessage(Msg, NULL, 0, 0) > 0)
{
TranslateMessage(Msg);
DispatchMessage(Msg);
}

Answer 1

Thre are two kind of hooks:
Global Hooks
Global hook procedures should be placed into a separate DLL, then in your main process you load the hook dll and it's hooking procedure and set the hook.
A global hook monitors messages for all threads in the same desktop as
the calling thread. A thread-specific hook monitors messages for only
an individual thread. A global hook procedure can be called in the
context of any application in the same desktop as the calling thread,
so the procedure must be in a separate DLL module.
That said: KeyboardProc goes into a separate DLL (e.g. myhookdll.dll).
In your process you do something like this:
HOOKPROC hkprc;
static HINSTANCE hhookDLL ;
static HHOOK hhook ;
hhookDLL = LoadLibrary(TEXT("c:\\...\\myhookdll.dll"));
hkprc = (HOOKPROC)GetProcAddress(hhookDLL, "KeyboardProc");
hhook = SetWindowsHookEx(
WH_KEYBOARD,
hkprc,
hhookDLL,
0);
Here a good reference: http://msdn.microsoft.com/en-us/library/windows/desktop/ms644960(v=vs.85).aspx
Thread Level Hooks about this specific 'WH_KEYBOARD_LL' that hooks at thread level, it does not need a separate DLL.
A thread-specific
hook procedure is called only in the context of the associated thread.
If an application installs a hook procedure for one of its own
threads, the hook procedure can be in either the same module as the
rest of the application's code or in a DLL. If the application
installs a hook procedure for a thread of a different application, the
procedure must be in a DLL. For information, see Dynamic-Link
Libraries.
But thread level hook needs a message pump:
This hook is called in the context of the thread that installed it.
The call is made by sending a message to the thread that installed the
hook. Therefore, the thread that installed the hook must have a
message loop.
Here a basic message loop:
while((bRet = GetMessage(&msg, NULL, 0, 0)) != 0)
{
if(bRet == -1)
{
// Handle Error
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}