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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>idempotent</title><link rel="stylesheet" href="../../jargon.css" type="text/css"/><meta name="generator" content="DocBook XSL Stylesheets V1.61.0"/><link rel="home" href="../index.html" title="The Jargon File"/><link rel="up" href="../I.html" title="I"/><link rel="previous" href="idiot.html" title="ID10T error"/><link rel="next" href="IDP.html" title="IDP"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">idempotent</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="idiot.html">Prev</a> </td><th width="60%" align="center">I</th><td width="20%" align="right"> <a accesskey="n" href="IDP.html">Next</a></td></tr></table><hr/></div><dt><a id="idempotent"/><dt xmlns="" id="idempotent"><b>idempotent</b>: <span xmlns="http://www.w3.org/1999/xhtml" class="grammar">adj.</span></dt></dt><dd><p> [from mathematical techspeak] Acting as if used only once, even if
used multiple times. This term is often used with respect to
<a href="../C/C.html"><i class="glossterm">C</i></a> header files, which contain common definitions and
declarations to be included by several source files. If a header file is
ever included twice during the same compilation (perhaps due to nested
#include files), compilation errors can result unless the header file has
protected itself against multiple inclusion; a header file so protected is
said to be idempotent. The term can also be used to describe an
initialization subroutine that is arranged to perform some critical action
exactly once, even if the routine is called several times.</p></dd><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="idiot.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="../I.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="IDP.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ID10T error </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> IDP</td></tr></table></div></body></html>