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230 lines
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230 lines
17 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>Create an anonymous (lambda-style) function</title>
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</head>
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<body class="docs"><div id="layout">
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<div id="layout-content"><div id="function.create-function" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">create_function</h1>
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<p class="verinfo">(PHP 4 >= 4.0.1, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">create_function</span> — <span class="dc-title">Create an anonymous (lambda-style) function</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.create-function-description">
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<h3 class="title">说明</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>create_function</strong></span>
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( <span class="methodparam"><span class="type">string</span> <code class="parameter">$args</code></span>
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, <span class="methodparam"><span class="type">string</span> <code class="parameter">$code</code></span>
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) : <span class="type">string</span></div>
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<p class="para rdfs-comment">
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Creates an anonymous function from the parameters passed, and
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returns a unique name for it.
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</p>
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<div class="caution"><strong class="caution">Caution</strong>
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<p class="para">
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This function internally performs an <span class="function"><a href="eval.html" class="function">eval()</a></span> and as such has the
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same security issues as <span class="function"><a href="eval.html" class="function">eval()</a></span>. Additionally it has bad performance
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and memory usage characteristics.
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</p>
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<p class="para">
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If you are using PHP 5.3.0 or newer a native
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<a href="functions.anonymous.html" class="link">anonymous function</a> should be used instead.
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</p>
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</div>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.create-function-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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Usually these parameters will be passed as single quote delimited strings.
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The reason for using single quoted strings, is to protect the variable
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names from parsing, otherwise, if you use double quotes there will be a
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need to escape the variable names, e.g. <em>\$avar</em>.
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<dl>
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<dt>
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<code class="parameter">args</code></dt>
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<dd>
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<p class="para">
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The function arguments.
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</p>
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</dd>
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<dt>
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<code class="parameter">code</code></dt>
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<dd>
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<p class="para">
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The function code.
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</p>
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</dd>
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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.create-function-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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Returns a unique function name as a string, or <strong><code>FALSE</code></strong> on error.
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.create-function-examples">
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<h3 class="title">范例</h3>
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<p class="para">
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<div class="example" id="example-6193">
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<p><strong>Example #1
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Creating an anonymous function with <span class="function"><strong>create_function()</strong></span>
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</strong></p>
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<div class="example-contents"><p>
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You can use this function, to (for example) create a function from
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information gathered at run time:
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</p></div>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$newfunc </span><span style="color: #007700">= </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$a,$b'</span><span style="color: #007700">, </span><span style="color: #DD0000">'return "ln($a) + ln($b) = " . log($a * $b);'</span><span style="color: #007700">);<br />echo </span><span style="color: #DD0000">"New anonymous function: </span><span style="color: #0000BB">$newfunc</span><span style="color: #DD0000">\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">$newfunc</span><span style="color: #007700">(</span><span style="color: #0000BB">2</span><span style="color: #007700">, </span><span style="color: #0000BB">M_E</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /></span><span style="color: #FF8000">// outputs<br />// New anonymous function: lambda_1<br />// ln(2) + ln(2.718281828459) = 1.6931471805599<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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</div>
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</p>
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<p class="para">
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Or, perhaps to have general handler function that can apply a set
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of operations to a list of parameters:
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</p>
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<p class="para">
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<div class="example" id="example-6194">
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<p><strong>Example #2
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Making a general processing function with
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<span class="function"><strong>create_function()</strong></span>
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</strong></p>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">process</span><span style="color: #007700">(</span><span style="color: #0000BB">$var1</span><span style="color: #007700">, </span><span style="color: #0000BB">$var2</span><span style="color: #007700">, </span><span style="color: #0000BB">$farr</span><span style="color: #007700">)<br />{<br /> foreach (</span><span style="color: #0000BB">$farr </span><span style="color: #007700">as </span><span style="color: #0000BB">$f</span><span style="color: #007700">) {<br /> echo </span><span style="color: #0000BB">$f</span><span style="color: #007700">(</span><span style="color: #0000BB">$var1</span><span style="color: #007700">, </span><span style="color: #0000BB">$var2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #FF8000">// create a bunch of math functions<br /></span><span style="color: #0000BB">$f1 </span><span style="color: #007700">= </span><span style="color: #DD0000">'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$f2 </span><span style="color: #007700">= </span><span style="color: #DD0000">"return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$f3 </span><span style="color: #007700">= </span><span style="color: #DD0000">'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$farr </span><span style="color: #007700">= array(<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$x,$y'</span><span style="color: #007700">, </span><span style="color: #DD0000">'return "some trig: ".(sin($x) + $x*cos($y));'</span><span style="color: #007700">),<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$x,$y'</span><span style="color: #007700">, </span><span style="color: #DD0000">'return "a hypotenuse: ".sqrt($x*$x + $y*$y);'</span><span style="color: #007700">),<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$a,$b'</span><span style="color: #007700">, </span><span style="color: #0000BB">$f1</span><span style="color: #007700">),<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$a,$b'</span><span style="color: #007700">, </span><span style="color: #0000BB">$f2</span><span style="color: #007700">),<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$a,$b'</span><span style="color: #007700">, </span><span style="color: #0000BB">$f3</span><span style="color: #007700">)<br /> );<br /><br />echo </span><span style="color: #DD0000">"\nUsing the first array of anonymous functions\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"parameters: 2.3445, M_PI\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">process</span><span style="color: #007700">(</span><span style="color: #0000BB">2.3445</span><span style="color: #007700">, </span><span style="color: #0000BB">M_PI</span><span style="color: #007700">, </span><span style="color: #0000BB">$farr</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// now make a bunch of string processing functions<br /></span><span style="color: #0000BB">$garr </span><span style="color: #007700">= array(<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$b,$a'</span><span style="color: #007700">, </span><span style="color: #DD0000">'if (strncmp($a, $b, 3) == 0) return "** \"$a\" '</span><span style="color: #007700">.<br /> </span><span style="color: #DD0000">'and \"$b\"\n** Look the same to me! (looking at the first 3 chars)";'</span><span style="color: #007700">),<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$a,$b'</span><span style="color: #007700">, </span><span style="color: #DD0000">'; return "CRCs: " . crc32($a) . ", ".crc32($b);'</span><span style="color: #007700">),<br /> </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$a,$b'</span><span style="color: #007700">, </span><span style="color: #DD0000">'; return "similar(a,b) = " . similar_text($a, $b, &$p) . "($p%)";'</span><span style="color: #007700">)<br /> );<br />echo </span><span style="color: #DD0000">"\nUsing the second array of anonymous functions\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">process</span><span style="color: #007700">(</span><span style="color: #DD0000">"Twas brilling and the slithy toves"</span><span style="color: #007700">, </span><span style="color: #DD0000">"Twas the night"</span><span style="color: #007700">, </span><span style="color: #0000BB">$garr</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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<div class="example-contents"><p>以上例程会输出：</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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Using the first array of anonymous functions
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parameters: 2.3445, M_PI
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some trig: -1.6291725057799
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a hypotenuse: 3.9199852871011
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b*a^2 = 4.8103313314525
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min(b^2+a, a^2,b) = 8.6382729035898
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ln(a)/b = 0.27122299212594
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Using the second array of anonymous functions
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** "Twas the night" and "Twas brilling and the slithy toves"
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** Look the same to me! (looking at the first 3 chars)
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CRCs: -725381282, 342550513
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similar(a,b) = 11(45.833333333333%)
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</pre></div>
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</div>
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</div>
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</p>
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<p class="para">
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But perhaps the most common use for of lambda-style (anonymous) functions
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is to create callback functions, for example when using
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<span class="function"><a href="array_walk.html" class="function">array_walk()</a></span> or <span class="function"><a href="usort.html" class="function">usort()</a></span>
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</p>
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<p class="para">
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<div class="example" id="example-6195">
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<p><strong>Example #3 Using anonymous functions as callback functions</strong></p>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$av </span><span style="color: #007700">= array(</span><span style="color: #DD0000">"the "</span><span style="color: #007700">, </span><span style="color: #DD0000">"a "</span><span style="color: #007700">, </span><span style="color: #DD0000">"that "</span><span style="color: #007700">, </span><span style="color: #DD0000">"this "</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">array_walk</span><span style="color: #007700">(</span><span style="color: #0000BB">$av</span><span style="color: #007700">, </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'&$v,$k'</span><span style="color: #007700">, </span><span style="color: #DD0000">'$v = $v . "mango";'</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">$av</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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<div class="example-contents"><p>以上例程会输出：</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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Array
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(
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[0] => the mango
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[1] => a mango
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[2] => that mango
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[3] => this mango
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)
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</pre></div>
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</div>
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<div class="example-contents"><p>
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an array of strings ordered from shorter to longer
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</p></div>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br /><br />$sv </span><span style="color: #007700">= array(</span><span style="color: #DD0000">"small"</span><span style="color: #007700">, </span><span style="color: #DD0000">"larger"</span><span style="color: #007700">, </span><span style="color: #DD0000">"a big string"</span><span style="color: #007700">, </span><span style="color: #DD0000">"it is a string thing"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">$sv</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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<div class="example-contents"><p>以上例程会输出：</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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Array
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(
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[0] => small
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[1] => larger
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[2] => a big string
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[3] => it is a string thing
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)
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</pre></div>
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</div>
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<div class="example-contents"><p>
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sort it from longer to shorter
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</p></div>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br /><br />usort</span><span style="color: #007700">(</span><span style="color: #0000BB">$sv</span><span style="color: #007700">, </span><span style="color: #0000BB">create_function</span><span style="color: #007700">(</span><span style="color: #DD0000">'$a,$b'</span><span style="color: #007700">,</span><span style="color: #DD0000">'return strlen($b) - strlen($a);'</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">$sv</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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<div class="example-contents"><p>以上例程会输出：</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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Array
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(
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[0] => it is a string thing
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[1] => a big string
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[2] => larger
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[3] => small
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)
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</pre></div>
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</div>
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</div>
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</p>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.create-function-seealso">
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<h3 class="title">参见</h3>
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<p class="para">
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<ul class="simplelist">
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<li class="member"><a href="functions.anonymous.html" class="link">Anonymous functions</a></li>
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</ul>
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</p>
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</div>
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</div></div></div></body></html> |