xseterrorhandler(3x) [hpux man page]

XSetErrorHandler()														XSetErrorHandler()

Name
  XSetErrorHandler - set a fatal error event handler.

Synopsis
  int (*XSetErrorHandler(handler))()
	int (* handler)(Display *)

Arguments
  handler   The  user-defined  function to be called to handle error events.  If a NULL pointer, reinvoke the default handler, which prints a
	    message and exits.

Returns
  The previous nonfatal error handler.

Description
  The error handler function specified in handler will be called by Xlib whenever an XError event is received.	 These	are  nonfatal  condi-
  tions,  such	as unexpected values for arguments, or a failure in server memory allocation.  It is acceptable for this procedure to return,
  though the default handler simply prints a message and exits.  However, the error handler should NOT perform any  operations	(directly  or
  indirectly) that generate protocol requests or that look for input events.

  In Release 4 and Release 5, XSetErrorHandler() returns a pointer to the previous error handler.

  The  function is called with two arguments:  the display variable and a pointer to the XErrorEvent structure.  Here is a trivial example of
  a user-defined error handler:
      int myhandler (display, myerr)
      Display *display;
      XErrorEvent *myerr;
      {
	 char msg[80];
	 XGetErrorText(display, myerr->error_code, msg, 80);
	 fprintf(stderr, "Error code %s
", msg);
      }

  This is how the example routine would be used in XSetErrorHandler():

      XSetErrorHandler(myhandler);

  Note that XSetErrorHandler() is one of the few routines that does not require a display argument.  The routine that calls the error handler
  gets the display variable from the XErrorEvent structure.

  The  error  handler is not called on BadName errors from OpenFont, LookupColor, and AllocNamedColor protocol requests, or on BadFont errors
  from a QueryFont protocol request.  These errors are all indicated by Status return value of zero in the corresponding Xlib routines, which
  must be caught and handled by the application.

  Use XIOErrorHandler to provide a handler for I/O errors such as network failures or server host crashes.

  In  the  XErrorEvent	structure shown below, the serial member is the number of requests (starting from 1) sent over the network connection
  since it was opened.	It is the number that was the value of the request sequence number immediately after the failing call was made.   The
  request_code member is a protocol representation of the name of the procedure that failed and is defined in <X11/Xproto.h>.

  For more information, see Volume One, Chapter 3, Basic Window Program.

Structures
     typedef struct {
	 int type
	 Display *display;	     /* display the event was read from */
	 XID resourceid;	     /* resource ID */
	 unsigned long serial;	     /* serial number of failed request */
	 unsigned char error_code;   /* error code of failed request */
	 unsigned char request_code; /* major opcode of failed request */
	 unsigned char minor_code;   /* minor opcode of failed request */
     } XErrorEvent;

See Also
  XDisplayName(), XGetErrorDatabaseText(), XGetErrorText(), XSetAfterFunction(), XSetIOErrorHandler(), XSynchronize().

Xlib - Error Handling														XSetErrorHandler()

XSetErrorHandler(3X11)						     MIT X11R4						    XSetErrorHandler(3X11)

Name
       XSetErrorHandler, XGetErrorText, XDisplayName, XSetIOErrorHandler, XGetErrorDatabaseText - default error handlers

Syntax
       int (*XSetErrorHandler(handler))()
	  int (*handler)(Display *, XErrorEvent *)

       XGetErrorText(display, code, buffer_return, length)
	  Display *display;
	  int code;
	  char *buffer_return;
	  int length;

       char *XDisplayName(string)
	  char *string;

       int (*XSetIOErrorHandler(handler))()
	  int (*handler)(Display *);

       XGetErrorDatabaseText(display, name, message, default_string, buffer_return, length)
	  Display *display;
	  char *name, *message;
	  char *default_string;
	  char *buffer_return;
	  int length;

Arguments
       buffer_return
		 Returns the error description.

       code	 Specifies the error code for which you want to obtain a description.

       default_string
		 Specifies the default error message if none is found in the database.

       display	 Specifies the connection to the X server.

       handler	 Specifies the program's supplied error handler.

       length	 Specifies the size of the buffer.

       message	 Specifies the type of the error message.

       name	 Specifies the name of the application.

       string	 Specifies the character string.

Description
       Xlib generally calls the program's supplied error handler whenever an error is received.  It is not called on errors from or protocol
       requests or on errors from a protocol request.  These errors generally are reflected back to the program through the procedural interface.
       Because this condition is not assumed to be fatal, it is acceptable for your error handler to return.  However, the error handler should
       not call any functions (directly or indirectly) on the display that will generate protocol requests or that will look for input events.
       The previous error handler is returned.

       The function copies a null-terminated string describing the specified error code into the specified buffer.  It is recommended that you use
       this function to obtain an error description because extensions to Xlib may define their own error codes and error strings.

       The function returns the name of the display that would attempt to use.	If a NULL string is specified, looks in the environment for the
       display and returns the display name that would attempt to use.	This makes it easier to report to the user precisely which display the
       program attempted to open when the initial connection attempt failed.

       The sets the fatal I/O error handler.  Xlib calls the program's supplied error handler if any sort of system call error occurs (for exam-
       ple, the connection to the server was lost).  This is assumed to be a fatal condition, and the called routine should not return.  If the
       I/O error handler does return, the client process exits.

       Note that the previous error handler is returned.

       The function returns a message (or the default message) from the error message database.  Xlib uses this function internally to look up its
       error messages.	On a UNIX-based system, the error message database is

       The name argument should generally be the name of your application.  The message argument should indicate which type of error message you
       want.  Xlib uses three predefined message types to report errors (uppercase and lowercase matter):

       XProtoError
		 The protocol error number is used as a string for the message argument.

       XlibMessage
		 These are the message strings that are used internally by the library.

       XRequest  For a core protocol request, the major request protocol number is used for the message argument.  For an extension request, the
		 extension name (as given by followed by a period (.) and the minor request protocol number is used for the message argument.  If
		 no string is found in the error database, the default_string is returned to the buffer argument.

See Also
       XOpenDisplay(3X11), XSynchronize(3X11)
       X Window System: The Complete Reference, Second Edition, Robert W. Scheifler and James Gettys

															    XSetErrorHandler(3X11)