void XtAppErrorMsg (app_context, name, type, class, default, params,
              num_params)
    XtAppContext app_context;
    String name;
    String type;
    String class;
    String default;
    String params;
    Cardinal num_params;
void XtAppSetErrorMsgHandler (app_context, msg_handler)
    XtAppContext app_context;
    XtErrorMsgHandler msg_handler;
void XtAppSetWarningMsgHandler (app_context, msg_handler)
    XtAppContext app_context;
    XtErrorMsgHandler msg_handler;
void XtAppWarningMsg  (app_context, name, type, class, default, params,
              num_params)
    XtAppContext app_context;
    String name;
    String type;
    String class;
    String default;
    String params;
    Cardinal num_params;
The XtAppSetErrorMsgHandler function registers the specified procedure, which is called when a fatal error occurs.
The XtAppSetWarningMsgHandler function registers the specified procedure, which is called when a nonfatal error condition occurs.
The XtAppWarningMsg function calls the high-level error handler and passes the specified information.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface