<HTML ><HEAD ><TITLE >isset</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.44"><LINK REL="HOME" TITLE="PHP Manual" HREF="manual.html"><LINK REL="UP" TITLE="Variable functions" HREF="ref.var.html"><LINK REL="PREVIOUS" TITLE="is_string" HREF="function.is-string.html"><LINK REL="NEXT" TITLE="print_r" HREF="function.print-r.html"></HEAD ><BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >PHP Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="function.is-string.html" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="function.print-r.html" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="function.isset" >isset</A ></H1 ><DIV CLASS="refnamediv" ><A NAME="AEN27622" ></A >isset -- determine whether a variable is set</DIV ><DIV CLASS="refsect1" ><A NAME="AEN27625" ></A ><H2 >Description</H2 ><DIV CLASS="funcsynopsis" ><P ></P ><CODE CLASS="FUNCDEF" >int isset</CODE >(mixed var);<P ></P ></DIV ><P > Returns true if <TT CLASS="parameter" ><I >var</I ></TT > exists; false otherwise. </P ><P > If a variable has been unset with <A HREF="function.unset.html" ><B CLASS="function" >unset()</B ></A >, it will no longer be <B CLASS="function" >isset()</B >. <DIV CLASS="informalexample" ><P ></P ><TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="programlisting" > 1 2 $a = "test"; 3 echo isset ($a); // true 4 unset ($a); 5 echo isset ($a); // false 6 </PRE ></TD ></TR ></TABLE ><P ></P ></DIV > </P ><P > See also <A HREF="function.empty.html" ><B CLASS="function" >empty()</B ></A > and <A HREF="function.unset.html" ><B CLASS="function" >unset()</B ></A >. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="function.is-string.html" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="manual.html" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="function.print-r.html" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >is_string</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ref.var.html" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >print_r</TD ></TR ></TABLE ></DIV ></BODY ></HTML >