<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Global Data in PL/Tcl</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.0.11 Documentation" HREF="index.html"><LINK REL="UP" TITLE="PL/Tcl - Tcl Procedural Language" HREF="pltcl.html"><LINK REL="PREVIOUS" TITLE="Data Values in PL/Tcl" HREF="pltcl-data.html"><LINK REL="NEXT" TITLE="Database Access from PL/Tcl" HREF="pltcl-dbaccess.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2007-02-02T03:57:22"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.0.11 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="pltcl-data.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="pltcl.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 36. PL/Tcl - Tcl Procedural Language</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="pltcl.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="pltcl-dbaccess.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="PLTCL-GLOBAL" >36.4. Global Data in PL/Tcl</A ></H1 ><A NAME="AEN33846" ></A ><P > Sometimes it is useful to have some global data that is held between two calls to a function or is shared between different functions. This is easily done since all PL/Tcl functions executed in one session share the same safe Tcl interpreter. So, any global Tcl variable is accessible to all PL/Tcl function calls and will persist for the duration of the SQL session. (Note that <SPAN CLASS="APPLICATION" >PL/TclU</SPAN > functions likewise share global data, but they are in a different Tcl interpreter and cannot communicate with PL/Tcl functions.) </P ><P > To help protect PL/Tcl functions from unintentionally interfering with each other, a global array is made available to each function via the <CODE CLASS="FUNCTION" >upvar</CODE > command. The global name of this variable is the function's internal name, and the local name is <TT CLASS="LITERAL" >GD</TT >. It is recommended that <TT CLASS="LITERAL" >GD</TT > be used for persistent private data of a function. Use regular Tcl global variables only for values that you specifically intend to be shared among multiple functions. </P ><P > An example of using <TT CLASS="LITERAL" >GD</TT > appears in the <CODE CLASS="FUNCTION" >spi_execp</CODE > example below. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="pltcl-data.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="pltcl-dbaccess.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Data Values in PL/Tcl</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="pltcl.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Database Access from PL/Tcl</TD ></TR ></TABLE ></DIV ></BODY ></HTML >