Process my WindowsHook before others - c++

Question

I have searched around on Google and the Microsoft hook documentation and I find plenty of how to make a hook, but I already know how to do that. How do I make my hook (keyboard hook in this case) be first in the queue to receive a message? I am trying to get my hook as close as hardware input as possible to prevent another keyhook from changing input.
I.E: App1 runs a key hook to spoof the flags of KBDLLHOOK to not be injected. How do I get to that message before they can change flags from LLKHF_INJECTED?
TL;DR How would my hook get the message before another to prevent key injection?
Simple code I am using to test
LRESULT CALLBACK keybdProc(int n, WPARAM w, LPARAM l)
{
KBDLLHOOKSTRUCT *kbdll = (KBDLLHOOKSTRUCT*)l;
if (w == WM_KEYDOWN)
{
switch (kbdll->flags)
{
case LLKHF_INJECTED:
printf("%d/%c is an Injected Key Press (Reject)\n", kbdll->vkCode, char(kbdll->vkCode));
break;
default:
printf("%d/%c Not injected (Continue)\n", kbdll->vkCode, char(kbdll->vkCode));
break;
}
}
return 0; //CallNextHookEx(NULL, n, w, l);
}
int main()
{
HHOOK keybdHk = SetWindowsHookEx(WH_KEYBOARD_LL, keybdProc, GetModuleHandle(NULL), 0);
MSG msg;
while (GetMessage(&msg, NULL, 0, 0)>0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
UnhookWindowsHookEx(keybdHk);
return 0;
}
edit: I am aware the message queue goes in last-first order, but somehow no matter if I start my program before or after App1 it still gets the input before my Keyhook and then doesn't call NextHook (So my hook never gets it) or it spoofs it.

Answer 1

Hooks are managed in hook chains, where hook procedures are executed in order, from front to back. As documented:
The SetWindowsHookEx function always installs a hook procedure at the beginning of a hook chain. When an event occurs that is monitored by a particular type of hook, the system calls the procedure at the beginning of the hook chain associated with the hook. Each hook procedure in the chain determines whether to pass the event to the next procedure.
To have your hook called first, it needs to be installed last. While this is easy to establish, maintaining that position in the hook chain is impossible to do.

Answer 2

Two things.
First:
As of Windows 10, the struct KBDLLHOOKSTRUCT that you receive in the lParam argument can no longer be modified. The changes you make to it are not passed to the next hook procedures, even if you call CallNextHookEx(NULL, code, wParam, lParam).
You could even pass a completely different lParam pointer to CallNextHookEx and yet the subsequent hooks will still receive the original, unmodified structure.
The ability to modify KBDLLHOOKSTRUCT has never been documented, but was indeed possible on previous versions of window. However, not any more.
However, you can still prevent other hook procedures from receiving the input message by simply not calling CallNextHookEx.
Second:
The appropriate way to avoid other processes from interfering with the input you see, is by using the Raw Input API.
You use the function RegisterRawInputDevices so that your process receives the input directly from the device. Other processes cannot block, tamper or alter in anyway what you get from this API.
With Raw Input you can even detect which specific keyboard sent a given keystroke (in case there's more than one keyboard plugged in), which is not possible using a keyboard hook.
This is how games detect their input, so that users can't inject fake keystrokes into the game using the SendInput function.