Understanding HOOKS

I have some code that monitors an Edit control and looks for the number 7 to be entered. When a 7 is entered, an action is taken.

I am new to c++, but want to understand each and every line of this code thoroughly.

To be fair, I will, of course break this down into multiple questions.

My first question about this code is:

[1] Can we go over the GetMsgProc function? A simple line by line explanation would be most beneficial.

Thank you! Although this code does work, I want to understand WHY.



and here is the code:

#include <windows.h>
HHOOK g_hhk;
HWND g_hEdit;

LRESULT CALLBACK GetMsgProc(
    int code,
    WPARAM wParam,
    LPARAM lParam
)
{
    if (0 > code || PM_NOREMOVE == wParam) return CallNextHookEx(g_hhk,code,wParam,lParam);

    MSG* pmsg = (MSG*) lParam;

    if (pmsg->message == WM_KEYDOWN) { // this one is for us

        if (pmsg->hwnd == g_hEdit && pmsg->wParam == VK_7) { // '7' has been pressed if the monitored edit control

            // ---> ACTION!
            MessageBox(NULL, "The number was pressed!", "Notice", MB_OK);
        }
    }

    return CallNextHookEx(g_hhk,code,wParam,lParam);
}

void InitMonitoring(HWND hEdit) {

    g_hEdit = hEdit;

    g_hhk = SetWindowsHookEx(WH_GETMESSAGE,GetMsgProc,NULL,GetCurrentThreadId());
}

void StopMonitoring() {

    UnhookWindowsHookEx(g_hhk);
}

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