Purpose of TranslateMessage and DispatchMessage while setting WH_KEYBOARD_LL hook

Question

I have just begun to learn how to set low level keyboard hooks in Windows using C++.

Here is a small code I have written to get started.

#include <iostream>
#include <windows.h>

HHOOK hook;

LRESULT CALLBACK keyboardHook(int nCode, WPARAM wParam, LPARAM lParam)
{
    KBDLLHOOKSTRUCT *p = (KBDLLHOOKSTRUCT *) lParam;
    std::cout << nCode << " - " << wParam << " - " << p->vkCode << std::endl;
    return CallNextHookEx(hook, nCode, wParam, lParam);
}

int main(int argc, char **argv)
{
    hook = SetWindowsHookEx(WH_KEYBOARD_LL, keyboardHook, NULL, NULL);
    if (hook == NULL) {
        std::cout << "Error " << GetLastError() << std::endl;
        return 1;
    }

    MSG messages;
    std::cout << "Waiting for messages ..." << std::endl;
    while (GetMessage (&messages, NULL, 0, 0))
    {
        std::cout << "Got message" << std::endl;
        TranslateMessage(&messages);
        std::cout << "Translated message" << std::endl;
        DispatchMessage(&messages);
        std::cout << "Dispatched message" << std::endl;
    }
    return 0;
}

I compile this in this manner:

vcvars32.bat
cl /D_WIN32_WINNT=0x0401 foo.cc /link user32.lib

When I execute the code and press A followed by B I get an output like the following:

C:\>foo
Waiting for messages ...
0 - 257 - 13
0 - 256 - 65
0 - 257 - 65
0 - 256 - 66
0 - 257 - 66

Why do I never see Got message in the output? Why does the control never enter the while loop? Can someone help me understand the purpose of GetMessage , TranslateMessage and DispatchMessage here? I have read the documentation, but I guess I am missing something because I fail to understand how they are useful since I am never able to invoke the body of the while loop.

Answer 1

The GetMessage() function waits until a message arrives for one of the windows created by your process. Since you have created no windows, you will receive no messages.