How can I toggle word-wrap in a multiline EditBox?
I can create it with or without but I don't know which message I should use to toggle the wrapping mode.
The EditBox does not support toggling word-wrap. There is no message you can send and you cannot change the window style because MSDN says:
After the control has been created, these styles cannot be modified, except as noted.
Your only option is to create a new control with the desired style (WS_HSCROLL|ES_AUTOHSCROLL), copy the text into the new control and then destroy the old control.
On Windows 2000 and later you can use EM_GETHANDLE+EM_SETHANDLE to swap the buffers without having to make a copy of the text.