How to Automatically Resize Rich Edit Controls
An application can resize a rich edit control as needed so that it is always the same size as its contents. A rich edit control supports this so-called bottomless functionality by sending its parent window an EN_REQUESTRESIZE notification code whenever the size of the control's content changes.
- Windows User Interface Programming
When processing the EN_REQUESTRESIZE notification code, an application should resize the control to the dimensions in the specified REQRESIZE structure. An application might also move any information that is near the control to accommodate the control's change in height. To resize the control, you can use the SetWindowPos function.