CB_GETLBTEXTLEN
wParam = (WPARAM) index; /* item index */
lParam = 0; /* not used, must be zero */
An application sends a CB_GETLBTEXTLEN message to retrieve the length of a string in the list box of a combo box.
index
Value of wParam. Specifies the zero-based index of the string.
The return value is the length of the string, in characters, excluding the terminating null character. If the index parameter does not specify a valid index, the return value is CB_ERR.
CB_GETLBTEXT