EM_SETHANDLE, EM_GETHANDLE 在没有 DS_LOCALEDIT 的情况下工作

Question

I made a program similar to Notepad using Visual Studio Community 2017 on Windows 10. It uses edit control created with CreateWindow with the following styles:

WS_CHILD | WS_VISIBLE | WS_HSCROLL | WS_VSCROLL 
| WS_BORDER | ES_LEFT | ES_MULTILINE | ES_AUTOHSCROLL | ES_AUTOVSCROLL

As you see, there's no DS_LOCALEDIT . However, using EM_SETHANDLE or EM_GETHANDLE to access the buffer within the edit control seems to work flawlessly. The following is a snippet of code that does initial buffer allocation for edit control that is supposed to have been created with DS_LOCALEDIT :

HLOCAL hEditMem = ::LocalAlloc(LPTR, sizeof(wchar_t) * 51);
wchar_t* pszEdit = reinterpret_cast<wchar_t*>(::LocalLock(hEditMem));
const std::wstring strData(L"Hello");
std::char_traits<wchar_t>::copy(pszEdit, strData.c_str(), strData.size());
::SendMessageW(hwndEdit, EM_SETHANDLE, reinterpret_cast<WPARAM>(hEditMem), 0);
::SendMessageW(hwndEdit, EM_SETMODIFY, TRUE, 0);

The documentation here clearly states that:

An application that uses the default allocation behavior (that is, does not use the
DS_LOCALEDIT style must not send EM_SETHANDLE and EM_GETHANDLE messages to the edit
control.

May be someone in Microsoft inconspicuously made the DS_LOCALEDIT no longer necessary as of Windows 10 or VS 2017 ?

Answer 1

Since no answer from anybody, I decided to answer my own ...

Using heuristic approach, I came to the following conclusions, which are unlike what's written on MSDN docs:

1. DS_LOCALEDIT is not a prerequisite for EM_SETHANDLE or EM_GETHANDLE, which means that the EM_XXXHANDLE can be used even when you're not managing the buffer customarily.
2. EM_GETHANDLE seems a far better choice than the WM_GETTEXT when all you need to do is just refer to a portion of text in edit control.
3. DS_LOCAEDIT seems to be obsolete, as I was able to set my own custom buffer without it. (As a side note, all I needed to do to increase the custom buffer, in response to EN_MAXTEXT, was to send EM_SETLIMITTEXT message with new size as parameter)

To me the second one was particularly important when implementing text find/replace using FindText and ReplaceText ; you don't want to copy all the text from the edit control, using WM_GETTEXT, just to search for certain keyword, would you?

I still haven't tested if plain old new can substitute LocalAlloc when setting custom buffer with EM_SETHANDLE.