man Tcl_UpVar () - link one variable to another
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
Interpreter containing variables; also used for error reporting. Identifies the stack frame containing source variable. May have any of the forms accepted by the upvar command, such as #0 or 1. Name of source variable, in the frame given by frameName. May refer to a scalar variable or to an array variable with a parenthesized index. 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. Either TCL_GLOBAL_ONLY or 0; if non-zero, then destName is a global variable; otherwise it is a local to the current procedure (or global if no procedure is active). First part of source variable's name (scalar name, or name of array without array index). If source variable is an element of an array, gives the index of the element. For scalar source variables, is NULL.
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 destination 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(2) (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