'\"
'\" Copyright (c) 1994 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" RCS: @(#) $Id: UpVar.3,v 1.7 2002/08/05 03:24:39 dgp Exp $
'\" 
.so man.macros
.TH Tcl_UpVar 3 7.4 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_UpVar, Tcl_UpVar2 \- link one variable to another
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_UpVar(\fIinterp, frameName, sourceName, destName, flags\fB)\fR
.sp
int
\fBTcl_UpVar2(\fIinterp, frameName, name1, name2, destName, flags\fB)\fR
.SH ARGUMENTS
.AS Tcl_VarTraceProc prevClientData
.AP Tcl_Interp *interp in
Interpreter containing variables;  also used for error reporting.
.AP "CONST char" *frameName in
Identifies the stack frame containing source variable.
May have any of the forms accepted by
the \fBupvar\fR command, such as \fB#0\fR or \fB1\fR.
.AP "CONST char" *sourceName in
Name of source variable, in the frame given by \fIframeName\fR.
May refer to a scalar variable or to an array variable with a
parenthesized index.
.AP "CONST char" *destName in
Name of destination variable, which is to be linked to source
variable so that references to \fIdestName\fR
refer to the other variable.  Must not currently exist except as
an upvar-ed variable.
.AP int flags in
Either TCL_GLOBAL_ONLY or 0;  if non-zero, then \fIdestName\fR is
a global variable;  otherwise it is a local to the current procedure
(or global if no procedure is active).
.AP "CONST char" *name1 in
First part of source variable's name (scalar name, or name of array
without array index).
.AP "CONST char" *name2 in
If source variable is an element of an array, gives the index of the element.
For scalar source variables, is NULL.
.BE

.SH DESCRIPTION
.PP
\fBTcl_UpVar\fR and \fBTcl_UpVar2\fR provide the same functionality
as the \fBupvar\fR command:  they make a link from a source variable
to a destination variable, so that references to the destination are
passed transparently through to the source.
The name of the source variable may be specified either as a single
string such as \fBxyx\fR or \fBa(24)\fR (by calling \fBTcl_UpVar\fR)
or in two parts where the array name has been separated from the
element name (by calling \fBTcl_UpVar2\fR).
The destination variable name is specified in a single string;  it
may not be an array element.
.PP
Both procedures return either TCL_OK or TCL_ERROR, and they
leave an error message in the interpreter's result if an error occurs.
.PP
As with the \fBupvar\fR command, the source variable need not exist;
if it does exist, unsetting it later does not destroy the link.  The
destination variable may exist at the time of the call, but if so
it must exist as a linked variable.

.SH KEYWORDS
linked variable, upvar, variable