WM_GETTEXTLENGTH
An
application sends a WM_GETTEXTLENGTH message to determine the length, in
characters, of the text associated with a window. The length does not include
the terminating null character.
WM_GETTEXTLENGTH
wParam = 0; // not used; must be zero
lParam = 0; // not used; must be zero
Parameters
This message
has no parameters.
Return Values
The return
value is the length, in characters, of the text.
Default Action
The DefWindowProc function returns the
length, in characters, of the text. Under certain conditions, this value may
actually be greater than the length of the text. For more information, see the
following Remarks section.
Remarks
For an edit control,
the text to be copied is the content of the edit control. For a combo box, the
text is the content of the edit control (or static-text) portion of the combo
box. For a button, the text is the button name. For other windows, the text is
the window title. To determine the length of an item in a list box, an
application can use the LB_GETTEXTLEN message.
Under certain
conditions, the DefWindowProc
function returns a value that 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 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.
See Also