XtGetSelectionValue, XtGetSelectionValues - obtain selection values
#include <X11/Intrinsic.h>
void XtGetSelectionValue(Widget w, Atom
    selection, Atom target, XtSelectionCallbackProc
    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 corresponding 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