Tcl_UpVar manual page - Tcl Library Procedures

## Tcl8.6.16/Tk8.6.16 Documentation > Tcl C API, version 8.6.16 > UpVar

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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
  DESCRIPTION
  KEYWORDS

### 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 variable. 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 frameName. 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 procedure (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 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(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
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