An application sends a WM_SETTEXT message to set the text of a window.
WM_SETTEXT wParam = 0; // not used; must be zero lParam = (LPARAM)(LPCTSTR)lpsz; // address of window-text string
The return value is TRUE if the text is set. It is FALSE (for an edit control), LB_ERRSPACE (for a list box), or CB_ERRSPACE (for a combo box) if insufficient space is available to set the text in the edit control. It is CB_ERR if this message is sent to a combo box without an edit control.
The DefWindowProc function sets and displays the window text.
For an edit control, the text is the contents of the edit control. For a combo box, the text is the contents of the edit-control portion of the combo box. For a button, the text is the button name. For other windows, the text is the window title.
This message does not change the current selection in the list box of a combo box. An application should use the CB_SELECTSTRING message to select the item in a list box that matches the text in the edit control.