function.function-exists.html
来自「php的帮助文档,涉及到PHP的案例和基本语法,以及实际应用内容」· HTML 代码 · 共 121 行
HTML
121 行
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Return TRUE if the given function has been defined</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.func-num-args.html">func_num_args</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.get-defined-functions.html">get_defined_functions</a></div> <div class="up"><a href="ref.funchand.html">Function handling Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="function.function-exists" class="refentry"> <div class="refnamediv"> <h1 class="refname">function_exists</h1> <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">function_exists</span> — <span class="dc-title">Return <b><tt>TRUE</tt></b> if the given function has been defined</span></p> </div> <div class="refsect1 description"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type">bool</span> <span class="methodname"><b><b>function_exists</b></b></span> ( <span class="methodparam"><span class="type">string</span> <tt class="parameter">$function_name</tt></span> )</div> <p class="para rdfs-comment"> Checks the list of defined functions, both built-in (internal) and user-defined, for <i><tt class="parameter">function_name</tt></i>. </p> </div> <div class="refsect1 parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt> <span class="term"><i><tt class="parameter">function_name</tt></i></span> <dd> <p class="para"> The function name, as a string. </p> </dd> </dt> </dl> </p> </div> <div class="refsect1 returnvalues"> <h3 class="title">Return Values</h3> <p class="para"> Returns <b><tt>TRUE</tt></b> if <i><tt class="parameter">function_name</tt></i> exists and is a function, <b><tt>FALSE</tt></b> otherwise. </p> <blockquote><p><b class="note">Note</b>: This function will return <b><tt>FALSE</tt></b> for constructs, such as <b>include_once()</b> and <a href="function.echo.html" class="function">echo()</a>. <br /> </p></blockquote> </div> <div class="refsect1 examples"> <h3 class="title">Examples</h3> <p class="para"> <div class="example"> <p><b>Example #1 <b>function_exists()</b> example</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">function_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'imap_open'</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #DD0000">"IMAP functions are available.<br />\n"</span><span style="color: #007700">;<br />} else {<br /> echo </span><span style="color: #DD0000">"IMAP functions are not available.<br />\n"</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> </div> <div class="refsect1 notes"> <h3 class="title">Notes</h3> <blockquote><p><b class="note">Note</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" class="link">image</a> functions being an example). <br /> </p></blockquote> </div> <div class="refsect1 seealso"> <h3 class="title">See Also</h3> <p class="para"> <ul class="simplelist"> <li class="member"><a href="function.method-exists.html" class="function" rel="rdfs-seeAlso">method_exists()</a></li> <li class="member"><a href="function.is-callable.html" class="function" rel="rdfs-seeAlso">is_callable()</a></li> <li class="member"><a href="function.get-defined-functions.html" class="function" rel="rdfs-seeAlso">get_defined_functions()</a></li> </ul> </p> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.func-num-args.html">func_num_args</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.get-defined-functions.html">get_defined_functions</a></div> <div class="up"><a href="ref.funchand.html">Function handling Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?