https://invisible-island.net/xterm/xtoolkit/
XtGetSelectionValue, XtGetSelectionValues - obtain selection values
#include <X11/Intrinsic.h>
void XtGetSelectionValue(Widget w, Atom selection, Atom target, XtSe-
lectionCallbackProc callback, XtPointer client_data, Time time);
void XtGetSelectionValues(Widget w, Atom selection, Atom *targets, int
count, XtSelectionCallbackProc callback, XtPointer *client_data,
Time time);
callback Specifies the callback procedure that is to be called when
the selection value has been obtained.
client_data
Specifies the argument that is to be passed to the specified
procedure when it is called.
client_data
Specifies the client data (one for each target type) that is
passed to the callback procedure when it is called for that
target.
count Specifies the length of the targets and client_data lists.
selection Specifies the particular selection desired (that is, primary
or secondary).
target Specifies the type of the information that is needed about
the selection.
targets Specifies the types of information that is needed about the
selection.
time Specifies the timestamp that indicates when the selection
value is desired.
w Specifies the widget that is making the request.
The XtGetSelectionValue function requests the value of the selection
that has been converted to the target type. The specified callback
will be called some time after XtGetSelectionValue is called; in fact,
it may be called before or after XtGetSelectionValue returns.
The XtGetSelectionValues function is similar to XtGetSelectionValue
except that it takes a list of target types and a list of client data
and obtains the current value of the selection converted to each of the
targets. The effect is as if each target were specified in a separate
call to XtGetSelectionValue. The callback is called once with the cor-
responding client data for each target. XtGetSelectionValues does
guarantee that all the conversions will use the same selection value
because the ownership of the selection cannot change in the middle of
the list, as would be when calling XtGetSelectionValue repeatedly.
XtAppGetSelectionTimeout(3), XtOwnSelection(3)
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtGetSelectionValue(3)