C child window procedure - c

Question

In C language, this is a child button window that I have put inside a window made with CreateWindowEx(). I am wondering if there's a way give this button window and ID so I can callback a procedure and make the button interactive for user experience.
Maybe implement it inside WM_COMMAND -> switch(LOWORD(wParam)){ case: THEIDOF_BUTTON}
This code runs under LRESULT CALLBACK window procedure of parent windows as you can see with WM_CREATE
HWND buttonBox;
case WM_CREATE:
(HWND)buttonBox = CreateWindow(WC_BUTTON, TEXT("ABUTTON"), WS_CHILD | WS_VISIBLE | WS_SIZEBOX, 500, 400, 300, 300, parentWindow, NULL, hInstance, NULL);

Answer 1

read about hMenu parameter in CreateWindowEx
A handle to a menu, or specifies a child-window identifier,
depending on the window style .. For a child window, hMenu specifies
the child-window identifier, an integer value used by a dialog box
control to notify its parent about events.
and from GetDlgCtrlID function documentation:
An application sets the identifier for a child window when it creates
the window by assigning the identifier value to the hmenu parameter
when calling the CreateWindow or CreateWindowEx function.
so you need next code for create child:
buttonBox = CreateWindow(WC_BUTTON, TEXT("ABUTTON"), WS_CHILD | WS_VISIBLE | WS_SIZEBOX,
500, 400, 300, 300, parentWindow, (HMENU)ID_BUTTON_BOX, hInstance, NULL);
where ID_BUTTON_BOX some integer value. and you get in back in WM_COMMAND as wParam (low word) or in WM_NOTIFY
here exist thin point - the CreateWindow[Ex] accept the LONG_PTR in place hMenu as child-window identifier. so 64-bit value on x64 system. the same result will be if call SetWindowLongPtr with GWLP_ID. we can call GetWindowLongPtr(buttonBox, GWLP_ID) after create and check that it return exactly ID_BUTTON_BOX. but if use GetDlgCtrlID function - it return (int)ID_BUTTON_BOX - truncated to 32-bit id.
in case WM_NOTIFY despite idFrom from NMHDR structure declared as UINT_PTR here really only truncated to 32-bit id because the GetDlgCtrlID used for initialize it.
the WM_COMMAND at all truncate id to low 16 bit in wParam.
so for example if we define ID_BUTTON_BOX as 0x9012345678 when calling the CreateWindow or CreateWindowEx function - we got back exactly 0x9012345678 if call GetWindowLongPtr(buttonBox, GWLP_ID). but GetDlgCtrlID(buttonBox) return already 0x12345678 only. also the 0x12345678 will be in wParam and idFrom when we handle WM_NOTIFY and on WM_COMMAND we got only 0x5678 as control id.
so despite we can set full 64 bit value for child window identifier (say pointer to some structure casted to ULONG_PTR) and get it back as is in call GetWindowLongPtr(buttonBox, GWLP_ID) - in WM_NOTIFY and WM_COMMAND we got back only low 32 or 16 bit of identifier. because this usually used only 16 bit values for child id

Answer 2

Once you have the HWND for your button, you must call SetWindowLongPtr to set the button ID:
HWND buttonBox;
#define ID_BUTTON_BOX (100) // or whatever you like, should be unique for the parent window.
//..
case WM_CREATE:
buttonBox = CreateWindow(WC_BUTTON, TEXT("ABUTTON"), WS_CHILD | WS_VISIBLE | WS_SIZEBOX, 500, 400, 300, 300, parentWindow, NULL, hInstance, NULL);
SetWindowLongPtr(buttonBox, GWL_ID, (LONG_PTR)ID_BUTTON_BOX);
Here's a link to the MSDN doc: https://msdn.microsoft.com/en-us/library/windows/desktop/ms644898(v=vs.85).aspx