XSetErrorHandler(3X11RISC/os Reference ManuXSetErrorHandler(3X11)



NAME
     XSetErrorHandler, XGetErrorText, XDisplayName, XSetIOEr-
     rorHandler, 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.





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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 proto-
     col 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 con-
     dition 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 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 condi-
     tion, 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 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.



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     XlibMessage
               These are the message strings that are used inter-
               nally 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 InitExtension) 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)
     Xlib - C Language X Interface







































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