https://invisible-island.net/xterm/xtoolkit/
XtError, XtSetErrorHandler, XtSetWarningHandler, XtWarning - low-level error handlers
#include <X11/Intrinsic.h> void XtError(const char *message); void XtSetErrorHandler(XtErrorHandler handler); void XtSetWarningHandler(XtErrorHandler handler); void XtWarning(const char *message);
message Specifies the nonfatal error message that is to be reported. handler Specifies the new fatal error procedure, which should not return, or the nonfatal error procedure, which usually returns. message Specifies the message that is to be reported.
The XtError function has been superceded by XtAppError. The XtSetErrorHandler function has been superceded by XtAppSetErrorHan- dler. The XtSetWarningHandler function has been superceded by XtAppSetWarn- ingHandler. The XtWarning function has been superceded by XtAppWarning.
XtAppError(3) X Toolkit Intrinsics – C Language Interface Xlib - C Language X Interface X Version 11 libXt 1.1.5.2 XtError(3)