An application sends an LB_GETTEXTLEN message to retrieve the length of a string in a list box.
LB_GETTEXTLEN wParam = (WPARAM) index; // item index lParam = 0; // not used; must be zero
Windows 95: The wParam parameter is limited to 16-bit values. This means list boxes cannot contain more than 32,767 items. Although the number of items is restricted, the total size in bytes of the items in a listbox is limited only by available memory.
The return value is the length of the string, in characters, excluding the terminating null character. Under certain conditions, this value may actually be greater than the length of the text. For more information, see the following Remarks section.
If the index parameter does not specify a valid index, the return value is LB_ERR.
Under certain conditions, the return value is larger than the actual length of the text. This occurs with certain mixtures of ANSI and Unicode, and is due to the operating system allowing for the possible existence of double-byte character set (DBCS) characters within the text. The return value, however, will always be at least as large as the actual length of the text; you can thus always use it to guide buffer allocation. This behavior can occur when an application uses both ANSI functions and common dialogs, which use Unicode.
To obtain the exact length of the text, use the WM_GETTEXT, LB_GETTEXT, or CB_GETLBTEXT messages, or the GetWindowText function.