<HTML><HEAD><TITLE>Built-In Commands - error manual page</TITLE></HEAD><BODY>
<H3><A NAME="M2">NAME</A></H3>
error - Generate an error
<H3><A NAME="M3">SYNOPSIS</A></H3>
<B>error </B><I>message</I> ?<I>info</I>? ?<I>code</I>?<BR>
<H3><A NAME="M4">DESCRIPTION</A></H3>
Returns a TCL_ERROR code, which causes command interpretation to be
unwound. <I>Message</I> is a string that is returned to the application
to indicate what went wrong.
<P>
If the <I>info</I> argument is provided and is non-empty,
it is used to initialize the global variable <B>errorInfo</B>.
<B>errorInfo</B> is used to accumulate a stack trace of what
was in progress when an error occurred; as nested commands unwind,
the Tcl interpreter adds information to <B>errorInfo</B>. If the
<I>info</I> argument is present, it is used to initialize
<B>errorInfo</B> and the first increment of unwind information
will not be added by the Tcl interpreter. In other
words, the command containing the <B>error</B> command will not appear
in <B>errorInfo</B>; in its place will be <I>info</I>.
This feature is most useful in conjunction with the <B><A HREF="../TkCmd/catch.htm">catch</A></B> command:
if a caught error cannot be handled successfully, <I>info</I> can be used
to return a stack trace reflecting the original point of occurrence
of the error:
<PRE><B>catch {...} errMsg
set savedInfo $errorInfo
...
error $errMsg $savedInfo</B></PRE>
<P>
If the <I>code</I> argument is present, then its value is stored
in the <B>errorCode</B> global variable. This variable is intended
to hold a machine-readable description of the error in cases where
such information is available; see the <B><A HREF="../TkCmd/tclvars.htm">tclvars</A></B> manual
page for information on the proper format for the variable.
If the <I>code</I> argument is not
present, then <B>errorCode</B> is automatically reset to
``NONE'' by the Tcl interpreter as part of processing the
error generated by the command.
<H3><A NAME="M5">SEE ALSO</A></H3>
<B><A HREF="../TkCmd/catch.htm">catch</A></B>, <B><A HREF="../TkCmd/tclvars.htm">tclvars</A></B>
<H3><A NAME="M6">KEYWORDS</A></H3>
<A href="../Keywords/E.htm#error">error</A>, <A href="../Keywords/E.htm#errorCode">errorCode</A>, <A href="../Keywords/E.htm#errorInfo">errorInfo</A>
<HR><PRE>
<A HREF="../copyright.htm">Copyright</A> © 1993 The Regents of the University of California.
<A HREF="../copyright.htm">Copyright</A> © 1994-1996 Sun Microsystems, Inc.
<A HREF="../copyright.htm">Copyright</A> © 1995-1997 Roger E. Critchlow Jr.</PRE>
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