XSetErrorHandler(XS)     X Version 11 (Release 5)       XSetErrorHandler(XS)
                                6 January 1993


 Name

    XSetErrorHandler - 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


    bufferreturn  Returns the error description.

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

    defaultstring 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 pro-
    tocol 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.  The returned text is in
    the encoding of the current locale.  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 XOpenDis-
    play 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.

    Note that the previous error handler is returned.

    The XGetErrorDatabaseText function returns a null-terminated message (or
    the default message) from the error message database.  Xlib uses this
    function internally to look up its error messages.  The defaultstring is
    assumed to be in the encoding of the current locale.  The bufferreturn
    text is in the encoding of the current locale.

    The name argument should generally be the name of your application.  The
    message argument should indicate which type of error message you want.
    If the name and message are not in the Host Portable Character Encoding
    the result is implementation dependent.  Xlib uses three predefined
    ``application names'' to report errors (uppercase and lowercase matter):

    XProtoError    The protocol error number is used as a string for the mes-
                   sage 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 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 defaultstring is
                   returned to the buffer argument.

 See also

    XOpenDisplay(XS), XSynchronize(XS)
    Xlib - C Language X Interface