EM_SETTARGETDEVICE message

Sets the target device and line width used for "what you see is what you get" (WYSIWYG) formatting in a rich edit control.

wParam

HDC for the target device.

lParam

Line width to use for formatting.

The return value is zero if the operation fails, or nonzero if it succeeds.

The HDC for the default printer can be obtained as follows.

PRINTDLG pd = { sizeof(pd) };
pd.Flags = PD_RETURNDC | PD_RETURNDEFAULT;
if (PrintDlg(&pd))
{
    HDC hdc = pd.hDC;
    ...
}

If lParam is zero, no line breaks are created.