CentOS 7.0 - man page for tcl_upvar2 (centos section 3)

Tcl_UpVar(3)			      Tcl Library Procedures			     Tcl_UpVar(3)

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NAME
       Tcl_UpVar, Tcl_UpVar2 - link one variable to another

SYNOPSIS
       #include <tcl.h>

       int
       Tcl_UpVar(interp, frameName, sourceName, destName, flags)

       int
       Tcl_UpVar2(interp, frameName, name1, name2, destName, flags)

ARGUMENTS
       Tcl_Interp *interp (in)		    Interpreter  containing  variables;   also	used  for
					    error reporting.

       const char *frameName (in)	    Identifies the stack frame	containing  source  vari-
					    able.   May  have  any  of	the forms accepted by the
					    upvar command, such as #0 or 1.

       const char *sourceName (in)	    Name of source variable, in the frame given by frame-
					    Name.   May refer to a scalar variable or to an array
					    variable with a parenthesized index.

       const char *destName (in)	    Name of destination variable, which is to  be  linked
					    to	source	variable  so  that references to destName
					    refer to the  other  variable.   Must  not	currently
					    exist except as an upvar-ed variable.

       int flags (in)			    One  of TCL_GLOBAL_ONLY, TCL_NAMESPACE_ONLY or 0;  if
					    non-zero, then destName  is  a  global  or	namespace
					    variable;	otherwise it is local to the current pro-
					    cedure (or	current  namespace  if	no  procedure  is
					    active).

       const char *name1 (in)		    First part of source variable's name (scalar name, or
					    name of array without array index).

       const char *name2 (in)		    If source variable is an element of an  array,  gives
					    the  index	of  the element.  For scalar source vari-
					    ables, is NULL.
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DESCRIPTION
       Tcl_UpVar and Tcl_UpVar2 provide the same functionality as the upvar command:  they make a
       link  from a source variable to a destination variable, so that references to the destina-
       tion are passed transparently through to the source.  The name of the source variable  may
       be  specified  either as a single string such as xyx or a(24) (by calling Tcl_UpVar) or in
       two parts where the array name has been	separated  from  the  element  name  (by  calling
       Tcl_UpVar2).   The  destination variable name is specified in a single string;  it may not
       be an array element.

       Both procedures return either TCL_OK or TCL_ERROR, and they leave an error message in  the
       interpreter's result if an error occurs.

       As with the upvar 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.

KEYWORDS
       linked variable, upvar, variable

Tcl					       7.4				     Tcl_UpVar(3)