does not go inside the Windows GetMessage loop on console application

Question

I want to detect keypress in C++ and i need to use Windows System Call. So, i did some research and this is what i got using Hooks and Message:

#include <Windows.h>
#include <iostream>
#include <sstream>
#include <fstream>
#include <ctime>

using namespace std;

LRESULT CALLBACK LowLevelKeyboardProc(int code, WPARAM wParam, LPARAM lParam) {
    if (code == HC_ACTION) {
        switch (wParam) {
        case WM_KEYDOWN:
            PKBDLLHOOKSTRUCT p = (PKBDLLHOOKSTRUCT)lParam;
            char c = char(MapVirtualKey(p->vkCode, MAPVK_VK_TO_CHAR));
            cout << c << endl;
        }
    }
    return CallNextHookEx(NULL, code, wParam, lParam);
}

int main() {    
    HHOOK HKeyboard = SetWindowsHookEx(WH_KEYBOARD_LL, LowLevelKeyboardProc, 0, 0);

    MSG msg;
    BOOL bRet;

    while ((bRet = GetMessage(&msg, NULL, 0, 0)) > 0) {
        cout << "bRet = " << bRet << endl; // I want to do something here, but the program doesn't seem to go in here
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    UnhookWindowsHookEx(HKeyboard);
    return 0;
}

My question is why my program doesn't go inside the loop(and instead stuck on GetMessage function)? I need it to set conditions to terminate after some seconds, so where should i put the conditions? I know the GetMessage function reads Message, but when i press keys on my keyboard it still not going in and the callback function works just fine.

That's fine. The hooking logic inside Windows is calling the hook proc directly - you just need the message loop so that Windows knows your service thread is in a known idle state. — 500 - Internal Server Error, Jan 30 '15 at 18:37
I see. But then, since it doesn't go inside the loop at all, can i just use `GetMessage(&msg, NULL, 0, 0)` instead of the whole loop? Also, if want to terminate after 10s, where would my "if process > 10s then terminate" code goes? — aufarg, Jan 31 '15 at 03:57

Ben Voigt · Accepted Answer · 2015-01-31T05:02:00.137

The events are posted to the active window. Console windows are owned by the console subsystem, csrss.exe, and it receives the events, then translates them to characters and puts them in the console object which is your application's stdin.

If you want to process events the Win32 GUI way, you should use a Win32 window (e.g. RegisterClass and CreateWindow), not a console window.

If you just want the callbacks to work for a certain period of time, you can use an alertable wait such as SleepEx or MsgWaitForMultipleObjects, which accept a timeout.

Blindy · Answer 2 · 2015-01-30T18:49:09.580

1

That's not surprising, there aren't really any messages on your thread queue and you have no window so there's no window queue either.

If you want to play with values returned from your hook, put the code in the hook callback function.

I should warn you that hooks like these won't work in console applications since the console window resides in another process. Also, if you look at the MSDN page for SetWindowsHookEx, you'll see that WH_KEYBOARD_LL is a global hook only, ie you have to put your hook handler in a DLL library and inject the hook in the other applications. Then you have to handle the 32/64 bit issue yourself.

And as a last note, when you say cout << c; in your handler, that would be printing in the process's output file handle, not your own.

edited Jan 30 '15 at 18:49

answered Jan 30 '15 at 18:43

Blindy

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I thought pressing keyboard generates message as per [link](https://msdn.microsoft.com/en-us/library/windows/desktop/ms644927%28v=vs.85%29.aspx#system_defined) "The system generates a message at each input event—for example, when the user types", did i understand it wrong? But then, why do my code works without DLL? – aufarg Jan 31 '15 at 04:01
@kucingimbalance: That link is correct, but it's not explaining some details that are relevant to your situation. The events are posted to the active window. Console windows are owned by the console subsystem, csrss.exe, and it receives the events, then translates them to characters and puts them in the console object which is your application's stdin. If you want to process events the Win32 GUI way, you should use a Win32 window, not a console window. – Ben Voigt Jan 31 '15 at 04:52

does not go inside the Windows GetMessage loop on console application

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