EM_STREAMIN

What do you usually do when you need to set text in a Windows control? You do one of the following:

• SetWindowText()
• SetDlgItemText()
• SendMessage(WM_SETTEXT)
• SendMessage(WM_SETTEXTEX)

It’s tempting to do the same for a Rich Edit control, and sure enough, this will work on almost all versions of Windows.

On early ‘98 systems, however, it won’t always work. In cases where it doesn’t, it either displays gobbledygook, does nothing, or crashes – pretty easy for this to slip by QA. Moreover, after looking into the MSDN documentation on the subject, I don’t actually see any guarantee that simply setting text on a Rich Edit control will work on any version of Windows.

Instead, you must stream text into these controls. Doing so is a little more cumbersome than a single function call, but it’s simple boilerplate code. Here is an example of how to do it:

static DWORD CALLBACK editStreamCallback(DWORD_PTR dwCookie,
                                         LPBYTE pbBuff,
                                         LONG cb,
                                         LONG *pcb)
{
    esstruct *ess = (esstruct *)dwCookie;
    if (NULL != ess) {
        *pcb = cb;
        if (*pcb > ess->nSize) {
            *pcb = ess->nSize;
        }
        if (*pcb > 0) {
            memcpy(pbBuff, ess->lpText, *pcb);
            ess->lpText += *pcb;
            ess->nSize -= *pcb;
        }
        return 0;
    }
    return ERROR_INVALID_PARAMETER;
}

void SetTextForMyControl(LPTSTR *text)
{
    esstruct ess;
    EDITSTREAM es;

    ess.lpText = text;
    ess.nSize = (text->get_Length()) * sizeof(TCHAR);

    es.dwCookie = (DWORD_PTR)&ess;
    es.dwError = 0;
    es.pfnCallback = editStreamCallback;

    SendMessage(GetDlgItem(hwnd, IDC_MYCONTROL),
        EM_STREAMIN,
        (WPARAM)(SF_TEXT /* optional: | SF_UNICODE*/),
        (LPARAM)&es);
}

This performs extremely reliably on all Windows systems I have tested. I strongly recommend that you use it whenever you want to set text on a Rich Edit control.

Sep 22, 2003