<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >function_exists</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="PHP 手册" HREF="index.html"><LINK REL="UP" TITLE="Function Handling Functions" HREF="ref.funchand.html"><LINK REL="PREVIOUS" TITLE="func_num_args" HREF="function.func-num-args.html"><LINK REL="NEXT" TITLE="get_defined_functions" HREF="function.get-defined-functions.html"><META HTTP-EQUIV="Content-type" CONTENT="text/html; charset=UTF-8"></HEAD ><BODY CLASS="refentry" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >PHP 手册</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="function.func-num-args.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="function.get-defined-functions.html" ACCESSKEY="N" >下一页</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="function.function-exists" ></A >function_exists</H1 ><DIV CLASS="refnamediv" ><A NAME="AEN62903" ></A ><P > (PHP 3 >= 3.0.7, PHP 4, PHP 5)</P >function_exists -- Return <TT CLASS="constant" ><B >TRUE</B ></TT > if the given function has been defined</DIV ><DIV CLASS="refsect1" ><A NAME="AEN62907" ></A ><H2 >说明</H2 >bool <B CLASS="methodname" >function_exists</B > ( string function_name )<BR ></BR ><P > Checks the list of defined functions, both built-in (internal) and user-defined, for <CODE CLASS="parameter" >function_name</CODE >. </P ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN62917" ></A ><H2 >参数</H2 ><P > <P ></P ><DIV CLASS="variablelist" ><DL ><DT ><CODE CLASS="parameter" >function_name</CODE ></DT ><DD ><P > The function name, as a string. </P ></DD ></DL ></DIV > </P ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN62926" ></A ><H2 >返回值</H2 ><P > Returns <TT CLASS="constant" ><B >TRUE</B ></TT > if <CODE CLASS="parameter" >function_name</CODE > exists and is a function, <TT CLASS="constant" ><B >FALSE</B ></TT > otherwise. </P ><DIV CLASS="note" ><BLOCKQUOTE CLASS="note" ><P ><B >注意: </B > This function will return <TT CLASS="constant" ><B >FALSE</B ></TT > for constructs, such as <A HREF="function.include-once.html" ><B CLASS="function" >include_once()</B ></A > and <A HREF="function.echo.html" ><B CLASS="function" >echo()</B ></A >. </P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN62937" ></A ><H2 >范例</H2 ><P > <TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" CLASS="EXAMPLE" ><TR ><TD ><DIV CLASS="example" ><A NAME="AEN62940" ></A ><P ><B >例 1. <B CLASS="function" >function_exists()</B > example</B ></P ><TABLE BORDER="0" BGCOLOR="#E0E0E0" CELLPADDING="5" ><TR ><TD ><code><font color="#000000"> <font color="#0000BB"><?php<br /></font><font color="#007700">if (</font><font color="#0000BB">function_exists</font><font color="#007700">(</font><font color="#DD0000">'imap_open'</font><font color="#007700">)) {<br /> echo </font><font color="#DD0000">"IMAP functions are available.<br />\n"</font><font color="#007700">;<br />} else {<br /> echo </font><font color="#DD0000">"IMAP functions are not available.<br />\n"</font><font color="#007700">;<br />}<br /></font><font color="#0000BB">?></font> </font> </code></TD ></TR ></TABLE ></DIV ></TD ></TR ></TABLE > </P ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN62944" ></A ><H2 >注释</H2 ><DIV CLASS="note" ><BLOCKQUOTE CLASS="note" ><P ><B >注意: </B > A function name may exist even if the function itself is unusable due to configuration or compiling options (with the <A HREF="ref.image.html" >image</A > functions being an example). </P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN62949" ></A ><H2 >参见</H2 ><P > <P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD ><A HREF="function.method-exists.html" ><B CLASS="function" >method_exists()</B ></A ></TD ></TR ><TR ><TD ><A HREF="function.is-callable.html" ><B CLASS="function" >is_callable()</B ></A ></TD ></TR ><TR ><TD ><A HREF="function.get-defined-functions.html" ><B CLASS="function" >get_defined_functions()</B ></A ></TD ></TR ></TBODY ></TABLE ><P ></P > </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="function.func-num-args.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >起始页</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="function.get-defined-functions.html" ACCESSKEY="N" >下一页</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >func_num_args</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" 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