CB_LIMITTEXT
wParam = (WPARAM) cchLimit; /* maximum number of characters */
lParam = 0; /* not used, must be zero */
An application sends a CB_LIMITTEXT message to limit the length of the text that the user may enter into the edit control of a combo box.
cchLimit
Value of wParam. Specifies the length, in characters, of the text the user can enter. If this parameter is zero, the text length is set to 65,535 characters.
The return value is 1 if the message is successful. If this message is sent to a combo box with the style CBS_DROPDOWNLIST, the return value is CB_ERR.
If the combo box does not have the style CBS_AUTOHSCROLL, setting the text limit to be larger than the size of the edit control will have no effect.
The CB_LIMITTEXT message limits only the text the user can enter. It has no effect on any text already in the edit control when the message is sent, nor does it affect the length of the text copied to the edit control when a string in the list box is selected.