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     X Version 11 (1 September 1988)         XSetErrorHandler(XS)



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


     SYNTAX
          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;

          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 BadName
          errors from OpenFont, LookupColor, or AllocNamedColor
          protocol requests or on BadFont errors from a QueryFont
          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 XGetErrorText 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 XDisplayName function returns the name of the display
          that XOpenDisplay would attempt to use.  If a NULL string is
          specified, XDisplayName looks in the environment for the
          display and returns the display name that XOpenDisplay 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 XSetIOErrorHandler sets the fatal I/O error handler.
          Xlib calls the program's supplied error handler if any sort
          of system call error occurs (for example, 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.

          The XGetErrorDatabaseText 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
          /usr/lib/X11/XErrorDB.

          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  The major 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
          XSynchronize(XS)
          Xlib - C Language X Interface


     (printed 2/12/90) (1 September 1988)    XSetErrorHandler(XS)