📄 function.eval.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Evaluate a string as PHP code</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.die.html">die</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.exit.html">exit</a></div> <div class="up"><a href="ref.misc.html">Misc. Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="function.eval" class="refentry"> <div class="refnamediv"> <h1 class="refname">eval</h1> <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">eval</span> — <span class="dc-title">Evaluate a string as PHP code</span></p> </div> <div class="refsect1 description"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <span class="methodname"><b><b>eval</b></b></span> ( <span class="methodparam"><span class="type">string</span> <tt class="parameter">$code_str</tt></span> )</div> <p class="para rdfs-comment"> Evaluates the string given in <i><tt class="parameter">code_str</tt></i> as PHP code. Among other things, this can be useful for storing code in a database text field for later execution. </p> <p class="para"> There are some factors to keep in mind when using <b>eval()</b>. Remember that the string passed must be valid PHP code, including things like terminating statements with a semicolon so the parser doesn't die on the line after the <b>eval()</b>, and properly escaping things in <i><tt class="parameter">code_str</tt></i>. To mix HTML output and PHP code you can use a closing PHP tag to leave PHP mode. </p> <p class="para"> Also remember that variables given values under <b>eval()</b> will retain these values in the main script afterwards. </p> </div> <div class="refsect1 parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt> <span class="term"><i><tt class="parameter">code_str</tt></i></span> <dd> <p class="para"> The code string to be evaluated. <i><tt class="parameter">code_str</tt></i> does not have to contain <a href="language.basic-syntax.html#language.basic-syntax.phpmode" class="link">PHP Opening tags</a>. </p> <p class="para"> A <i>return</i> statement will immediately terminate the evaluation of the string . </p> </dd> </dt> </dl> </p> </div> <div class="refsect1 returnvalues"> <h3 class="title">Return Values</h3> <p class="para"> <b>eval()</b> returns <b><tt>NULL</tt></b> unless <i>return</i> is called in the evaluated code, in which case the value passed to <i>return</i> is returned. If there is a parse error in the evaluated code, <b>eval()</b> returns <b><tt>FALSE</tt></b> and execution of the following code continues normally. It is not possible to catch a parse error in <b>eval()</b> using <a href="function.set-error-handler.html" class="function">set_error_handler()</a>. </p> </div> <div class="refsect1 examples"> <h3 class="title">Examples</h3> <p class="para"> <div class="example"> <p><b>Example #1 <b>eval()</b> example - simple text merge</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />$string </span><span style="color: #007700">= </span><span style="color: #DD0000">'cup'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$name </span><span style="color: #007700">= </span><span style="color: #DD0000">'coffee'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$str </span><span style="color: #007700">= </span><span style="color: #DD0000">'This is a $string with my $name in it.'</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">$str</span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />eval(</span><span style="color: #DD0000">"\$str = \"$str\";"</span><span style="color: #007700">);<br />echo </span><span style="color: #0000BB">$str</span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> <div class="example-contents"><p>The above example will output:</p></div> <div class="example-contents"><pre><div class="cdata"><pre>This is a $string with my $name in it.This is a cup with my coffee in it.</pre></div> </pre></div> </div> </p> </div> <div class="refsect1 notes"> <h3 class="title">Notes</h3> <blockquote><p><b class="note">Note</b>: <span class="simpara">Because this is a language construct and not a function, it cannot be called using <a href="functions.variable-functions.html" class="link">variable functions</a></span></p></blockquote> <div class="tip"><b class="tip">Tip</b><p class="simpara">As with anything that outputsits result directly to the browser, the <a href="ref.outcontrol.html" class="link">output-control functions</a> can be used to capturethe output of this function, and save it in a<a href="language.types.string.html" class="type string">string</a> (for example).</p></div> <blockquote><p><b class="note">Note</b>: In case of a fatal error in the evaluated code, the whole script exits. <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.call-user-func.html" class="function" rel="rdfs-seeAlso">call_user_func()</a></li> </ul> </p> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.die.html">die</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.exit.html">exit</a></div> <div class="up"><a href="ref.misc.html">Misc. 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
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -