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<!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>返回字符串的子串</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.substr" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">substr</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">substr</span> — <span class="dc-title">返回字符串的子串</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.substr-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>substr</strong></span>
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( <span class="methodparam"><span class="type">string</span> <code class="parameter">$string</code></span>
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, <span class="methodparam"><span class="type">int</span> <code class="parameter">$start</code></span>
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[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$length</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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返回字符串 <code class="parameter">string</code> 由 <code class="parameter">start</code> 和 <code class="parameter">length</code> 参数指定的子字符串。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.substr-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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<dl>
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<dt>
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<code class="parameter">string</code></dt>
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<dd>
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<p class="para">
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输入字符串。必须至少有一个字符。
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</p>
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</dd>
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<dt>
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<code class="parameter">start</code></dt>
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<dd>
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<p class="para">
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如果 <code class="parameter">start</code> 是非负数，返回的字符串将从 <code class="parameter">string</code> 的 <code class="parameter">start</code> 位置开始，从 0 开始计算。例如，在字符串 “<em>abcdef</em>” 中，在位置 <em>0</em> 的字符是 “<em>a</em>”，位置 <em>2</em> 的字符串是 “<em>c</em>” 等等。
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</p>
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<p class="para">
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如果 <code class="parameter">start</code> 是负数，返回的字符串将从 <code class="parameter">string</code> 结尾处向前数第 <code class="parameter">start</code> 个字符开始。
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</p>
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<p class="para">
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如果 <code class="parameter">string</code> 的长度小于 <code class="parameter">start</code>，将返回 <strong><code>FALSE</code></strong>。
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</p>
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<p class="para">
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<div class="example" id="example-5995">
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<p><strong>Example #1 使用负数 <code class="parameter">start</code></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 />$rest </span><span style="color: #007700">= </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"abcdef"</span><span style="color: #007700">, -</span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// 返回 "f"<br /></span><span style="color: #0000BB">$rest </span><span style="color: #007700">= </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"abcdef"</span><span style="color: #007700">, -</span><span style="color: #0000BB">2</span><span style="color: #007700">); </span><span style="color: #FF8000">// 返回 "ef"<br /></span><span style="color: #0000BB">$rest </span><span style="color: #007700">= </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"abcdef"</span><span style="color: #007700">, -</span><span style="color: #0000BB">3</span><span style="color: #007700">, </span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// 返回 "d"<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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</dd>
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<dt>
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<code class="parameter">length</code></dt>
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<dd>
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<p class="para">
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如果提供了正数的 <code class="parameter">length</code>，返回的字符串将从 <code class="parameter">start</code> 处开始最多包括 <code class="parameter">length</code> 个字符（取决于 <code class="parameter">string</code> 的长度）。
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</p>
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<p class="para">
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如果提供了负数的 <code class="parameter">length</code>，那么 <code class="parameter">string</code> 末尾处的 <code class="parameter">length</code> 个字符将会被省略（若 <code class="parameter">start</code> 是负数则从字符串尾部算起）。如果 <code class="parameter">start</code> 不在这段文本中，那么将返回 <strong><code>FALSE</code></strong>。
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</p>
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<p class="para">
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如果提供了值为 <em>0</em>，<strong><code>FALSE</code></strong> 或 <strong><code>NULL</code></strong> 的 <code class="parameter">length</code>，那么将返回一个空字符串。
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</p>
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<p class="para">
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如果没有提供 <code class="parameter">length</code>，返回的子字符串将从 <code class="parameter">start</code> 位置开始直到字符串结尾。
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</p>
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<div class="example" id="example-5996">
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<p><strong>Example #2 使用负数 <code class="parameter">length</code></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 />$rest </span><span style="color: #007700">= </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"abcdef"</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, -</span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// 返回 "abcde"<br /></span><span style="color: #0000BB">$rest </span><span style="color: #007700">= </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"abcdef"</span><span style="color: #007700">, </span><span style="color: #0000BB">2</span><span style="color: #007700">, -</span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// 返回 "cde"<br /></span><span style="color: #0000BB">$rest </span><span style="color: #007700">= </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"abcdef"</span><span style="color: #007700">, </span><span style="color: #0000BB">4</span><span style="color: #007700">, -</span><span style="color: #0000BB">4</span><span style="color: #007700">); </span><span style="color: #FF8000">// 返回 ""<br /></span><span style="color: #0000BB">$rest </span><span style="color: #007700">= </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"abcdef"</span><span style="color: #007700">, -</span><span style="color: #0000BB">3</span><span style="color: #007700">, -</span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// 返回 "de"<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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</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.substr-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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返回提取的子字符串， 或者在失败时返回 <strong><code>FALSE</code></strong>。
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</p>
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</div>
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<div class="refsect1 changelog" id="refsect1-function.substr-changelog">
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<h3 class="title">更新日志</h3>
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<p class="para">
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<table class="doctable informaltable">
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<thead>
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<tr>
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<th>版本</th>
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<th>说明</th>
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</tr>
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</thead>
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<tbody class="tbody">
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<tr>
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<td>7.0.0</td>
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<td>
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如果 <code class="parameter">string</code> 的字符串长度与
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<code class="parameter">start</code> 相同时将返回一个空字符串。在之前的版本中，这种情况将返回 <strong><code>FALSE</code></strong> 。
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</td>
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</tr>
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<tr>
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<td>5.2.2 - 5.2.6</td>
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<td>
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If the <code class="parameter">start</code> parameter indicates the position of
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a negative truncation or beyond, false is returned. Other versions get
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the string from start.
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</td>
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</tr>
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</tbody>
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</table>
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.substr-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-5997">
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<p><strong>Example #3 <span class="function"><strong>substr()</strong></span> 基本用法</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">echo </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">'abcdef'</span><span style="color: #007700">, </span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// bcdef<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">'abcdef'</span><span style="color: #007700">, </span><span style="color: #0000BB">1</span><span style="color: #007700">, </span><span style="color: #0000BB">3</span><span style="color: #007700">); </span><span style="color: #FF8000">// bcd<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">'abcdef'</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">4</span><span style="color: #007700">); </span><span style="color: #FF8000">// abcd<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">'abcdef'</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">8</span><span style="color: #007700">); </span><span style="color: #FF8000">// abcdef<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">'abcdef'</span><span style="color: #007700">, -</span><span style="color: #0000BB">1</span><span style="color: #007700">, </span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// f<br /><br />// 访问字符串中的单个字符<br />// 也可以使用中括号<br /></span><span style="color: #0000BB">$string </span><span style="color: #007700">= </span><span style="color: #DD0000">'abcdef'</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">$string</span><span style="color: #007700">[</span><span style="color: #0000BB">0</span><span style="color: #007700">]; </span><span style="color: #FF8000">// a<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">$string</span><span style="color: #007700">[</span><span style="color: #0000BB">3</span><span style="color: #007700">]; </span><span style="color: #FF8000">// d<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">$string</span><span style="color: #007700">[</span><span style="color: #0000BB">strlen</span><span style="color: #007700">(</span><span style="color: #0000BB">$string</span><span style="color: #007700">)-</span><span style="color: #0000BB">1</span><span style="color: #007700">]; </span><span style="color: #FF8000">// f<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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<div class="example" id="example-5998">
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<p><strong>Example #4 <span class="function"><strong>substr()</strong></span> casting behaviour</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">class </span><span style="color: #0000BB">apple </span><span style="color: #007700">{<br /> public function </span><span style="color: #0000BB">__toString</span><span style="color: #007700">() {<br /> return </span><span style="color: #DD0000">"green"</span><span style="color: #007700">;<br /> }<br />}<br /><br />echo </span><span style="color: #DD0000">"1) "</span><span style="color: #007700">.</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">"pear"</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">2</span><span style="color: #007700">), </span><span style="color: #0000BB">true</span><span style="color: #007700">).</span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"2) "</span><span style="color: #007700">.</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #0000BB">54321</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">2</span><span style="color: #007700">), </span><span style="color: #0000BB">true</span><span style="color: #007700">).</span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"3) "</span><span style="color: #007700">.</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(new </span><span style="color: #0000BB">apple</span><span style="color: #007700">(), </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">2</span><span style="color: #007700">), </span><span style="color: #0000BB">true</span><span style="color: #007700">).</span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"4) "</span><span style="color: #007700">.</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #0000BB">true</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">1</span><span style="color: #007700">), </span><span style="color: #0000BB">true</span><span style="color: #007700">).</span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"5) "</span><span style="color: #007700">.</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #0000BB">false</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">1</span><span style="color: #007700">), </span><span style="color: #0000BB">true</span><span style="color: #007700">).</span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"6) "</span><span style="color: #007700">.</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">""</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">1</span><span style="color: #007700">), </span><span style="color: #0000BB">true</span><span style="color: #007700">).</span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"7) "</span><span style="color: #007700">.</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #0000BB">1.2e3</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">, </span><span style="color: #0000BB">4</span><span style="color: #007700">), </span><span style="color: #0000BB">true</span><span style="color: #007700">).</span><span style="color: #0000BB">PHP_EOL</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>Output of the above example in PHP 7:</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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1) 'pe'
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2) '54'
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3) 'gr'
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4) '1'
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5) false
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6) false
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7) '1200'
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</pre></div>
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</div>
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<div class="example-contents"><p>Output of the above example in PHP 5:</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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1) 'pe'
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2) '54'
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3) 'gr'
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4) '1'
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5) false
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6) false
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7) '1200'
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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 errors" id="refsect1-function.substr-errors">
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<h3 class="title">错误／异常</h3>
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<p class="para">
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错误时返回 <strong><code>FALSE</code></strong>。
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<div class="example" id="example-5999">
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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 />var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">substr</span><span style="color: #007700">(</span><span style="color: #DD0000">'a'</span><span style="color: #007700">, </span><span style="color: #0000BB">2</span><span style="color: #007700">)); </span><span style="color: #FF8000">// bool(false)<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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</div>
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<div class="refsect1 seealso" id="refsect1-function.substr-seealso">
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<h3 class="title">参见</h3>
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<p class="para">
|
||
<ul class="simplelist">
|
||
<li class="member"><span class="function"><a href="strrchr.html" class="function" rel="rdfs-seeAlso">strrchr()</a> - 查找指定字符在字符串中的最后一次出现</span></li>
|
||
<li class="member"><span class="function"><a href="substr_replace.html" class="function" rel="rdfs-seeAlso">substr_replace()</a> - 替换字符串的子串</span></li>
|
||
<li class="member"><span class="function"><a href="preg_match.html" class="function" rel="rdfs-seeAlso">preg_match()</a> - 执行匹配正则表达式</span></li>
|
||
<li class="member"><span class="function"><a href="trim.html" class="function" rel="rdfs-seeAlso">trim()</a> - 去除字符串首尾处的空白字符（或者其他字符）</span></li>
|
||
<li class="member"><span class="function"><a href="mb_substr.html" class="function" rel="rdfs-seeAlso">mb_substr()</a> - 获取部分字符串</span></li>
|
||
<li class="member"><span class="function"><a href="wordwrap.html" class="function" rel="rdfs-seeAlso">wordwrap()</a> - 打断字符串为指定数量的字串</span></li>
|
||
<li class="member"><a href="language.types.string.html#language.types.string.substr" class="link">字符串访问和修改</a></li>
|
||
</ul>
|
||
</p>
|
||
</div>
|
||
|
||
|
||
</div></div></div></body></html> |