https://invisible-island.net/xterm/xtoolkit/
XtAddCallback, XtAddCallbacks, XtRemoveCallback, XtRemoveCallbacks,
XtRemoveAllCallbacks - add and remove callback procedures
#include <X11/Intrinsic.h>
void XtAddCallback(Widget w, const char *callback_name, XtCallbackProc
callback, XtPointer client_data);
void XtAddCallbacks(Widget w, const char *callback_name, XtCallbackList
callbacks);
void XtRemoveCallback(Widget w, const char *callback_name, XtCallback-
Proc callback, XtPointer client_data);
void XtRemoveCallbacks(Widget w, const char *callback_name, XtCallback-
List callbacks);
void XtRemoveAllCallbacks(Widget w, const char *callback_name);
callback Specifies the callback procedure.
callbacks Specifies the null-terminated list of callback procedures and
corresponding client data.
callback_name
Specifies the callback list to which the procedure is to be
appended or deleted.
client_data
Specifies the argument that is to be passed to the specified
procedure when it is invoked by XtCallbacks or NULL, or the
client data to match on the registered callback procedures.
w Specifies the widget.
The XtAddCallback function adds the specified callback procedure to the
specified widget's callback list.
The XtAddCallbacks add the specified list of callbacks to the specified
widget's callback list.
The XtRemoveCallback function removes a callback only if both the pro-
cedure and the client data match.
The XtRemoveCallbacks function removes the specified callback proce-
dures from the specified widget's callback list.
The XtRemoveAllCallbacks function removes all the callback procedures
from the specified widget's callback list.
XtCallCallbacks(3)
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtAddCallback(3)