69 lines
3.7 KiB
HTML
69 lines
3.7 KiB
HTML
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<HTML><HEAD><TITLE>Tcl Built-In Commands - bgerror manual page</TITLE></HEAD><BODY>
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<H3><A NAME="M2">NAME</A></H3>
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bgerror - Command invoked to process background errors
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<H3><A NAME="M3">SYNOPSIS</A></H3>
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<B>bgerror </B><I>message</I><BR>
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<H3><A NAME="M4">DESCRIPTION</A></H3>
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The <B>bgerror</B> command doesn't exist as built-in part of Tcl. Instead,
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individual applications or users can define a <B>bgerror</B>
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command (e.g. as a Tcl procedure) if they wish to handle background
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errors.
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<P>
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A background error is one that occurs in an event handler or some
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other command that didn't originate with the application.
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For example, if an error occurs while executing a command specified
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with the <B><A HREF="../TkCmd/after.htm">after</A></B> command, then it is a background error.
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For a non-background error, the error can simply be returned up
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through nested Tcl command evaluations until it reaches the top-level
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code in the application; then the application can report the error
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in whatever way it wishes. When a background error occurs, the
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unwinding ends in the Tcl library and there is no obvious way for Tcl
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to report the error.
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<P>
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When Tcl detects a background error, it saves information about the
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error and invokes the <B>bgerror</B> command later as an idle event
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handler. Before invoking <B>bgerror</B>, Tcl restores the
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<B>errorInfo</B> and <B>errorCode</B> variables to their values at the
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time the error occurred, then it invokes <B>bgerror</B> with the error
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message as its only argument. Tcl assumes that the application has
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implemented the <B>bgerror</B> command, and that the command will
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report the error in a way that makes sense for the application. Tcl
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will ignore any result returned by the <B>bgerror</B> command as long
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as no error is generated.
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<P>
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If another Tcl error occurs within the <B>bgerror</B> command (for
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example, because no <B>bgerror</B> command has been defined) then Tcl
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reports the error itself by writing a message to stderr.
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<P>
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If several background errors accumulate before <B>bgerror</B> is
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invoked to process them, <B>bgerror</B> will be invoked once for each
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error, in the order they occurred. However, if <B>bgerror</B> returns
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with a break exception, then any remaining errors are skipped without
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calling <B>bgerror</B>.
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<P>
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Tcl has no default implementation for <B>bgerror</B>. However, in
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applications using Tk there is a default <B>bgerror</B> procedure which
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posts a dialog box containing the error message and offers the user a
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chance to see a stack trace showing where the error occurred. In
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addition to allowing the user to view the stack trace, the dialog
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provides an additional application configurable button which may be
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used, for example, to save the stack trace to a file. By default,
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this is the behavior associated with that button. This behavior can
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be redefined by setting the option database values
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<B>*ErrorDialog.function.text</B>, to specify the caption for the
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function button, and <B>*ErrorDialog.function.command</B>, to specify
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the command to be run. The text of the stack trace is appended to the
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command when it is evaluated. If either of these options is set to
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the empty string, then the additional button will not be displayed in
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the dialog.
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<H3><A NAME="M5">SEE ALSO</A></H3>
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<B><A HREF="../TkCmd/after.htm">after</A></B>, <B><A HREF="../TkCmd/tclvars.htm">tclvars</A></B>
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<H3><A NAME="M6">KEYWORDS</A></H3>
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<A href="../Keywords/B.htm#background error">background error</A>, <A href="../Keywords/R.htm#reporting">reporting</A>
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<HR><PRE>
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<A HREF="../copyright.htm">Copyright</A> © 1990-1994 The Regents of the University of California.
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<A HREF="../copyright.htm">Copyright</A> © 1994-1996 Sun Microsystems, Inc.
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<A HREF="../copyright.htm">Copyright</A> © 1995-1997 Roger E. Critchlow Jr.</PRE>
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</BODY></HTML>
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