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175 lines
8.5 KiB
HTML
175 lines
8.5 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>简介</title>
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</head>
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<div id="layout">
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<div id="layout-content"><div id="language.types.intro" class="sect1">
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<h2 class="title">简介</h2>
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<p class="simpara">
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PHP 支持 9 种原始数据类型。
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</p>
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<p class="para">
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四种标量类型：
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</p>
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<ul class="itemizedlist">
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.boolean.html" class="type boolean">boolean</a></span>（布尔型）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span>（整型）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.float.html" class="type float">float</a></span>（浮点型，也称作 <span class="type"><a href="language.types.float.html" class="type double">double</a></span>)
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.string.html" class="type string">string</a></span>（字符串）
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</span>
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</li>
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</ul>
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<p class="para">
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三种复合类型：
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</p>
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<ul class="itemizedlist">
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.array.html" class="type array">array</a></span>（数组）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.object.html" class="type object">object</a></span>（对象）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.callable.html" class="type callable">callable</a></span>（可调用）
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</span>
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</li>
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</ul>
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<p class="para">
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最后是两种特殊类型：
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</p>
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<ul class="itemizedlist">
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span>（资源）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.types.null.html" class="type NULL">NULL</a></span>（无类型）
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</span>
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</li>
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</ul>
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<p class="para">
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为了确保代码的易读性，本手册还介绍了一些<a href="language.pseudo-types.html" class="link">伪类型</a>：
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</p>
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<ul class="itemizedlist">
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span>（混合类型）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.pseudo-types.html#language.types.number" class="type number">number</a></span>（数字类型）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.pseudo-types.html#language.types.callback" class="type callback">callback</a></span>（回调类型，又称为 <span class="type"><a href="language.types.callable.html" class="type callable">callable</a></span>）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><a href="language.pseudo-types.html#language.types.array-object" class="type array|object">array|object</a></span>（数组 | 对象类型）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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<span class="type"><span class="type void">void</span></span> （无类型）
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</span>
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</li>
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</ul>
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<p class="para">
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以及伪变量 <code class="parameter">$...</code>。
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</p>
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<p class="simpara">
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可能还会读到一些关于“双精度（double）”类型的参考。实际上
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double 和 float 是相同的，由于一些历史的原因，这两个名称同时存在。
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</p>
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<p class="simpara">
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变量的类型通常不是由程序员设定的，确切地说，是由 PHP
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根据该变量使用的上下文在运行时决定的。
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</p>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<span class="simpara">
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如果想查看某个<a href="language.expressions.html" class="link">表达式</a>的值和类型，用
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<span class="function"><a href="var_dump.html" class="function">var_dump()</a></span> 函数。
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</span>
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<p class="para">
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如果只是想得到一个易读懂的类型的表达方式用于调试，用
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<span class="function"><a href="gettype.html" class="function">gettype()</a></span> 函数。要检验某个类型，<em class="emphasis">不要</em>用
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<span class="function"><a href="gettype.html" class="function">gettype()</a></span>，而用 <em>is_<span class="replaceable">type</span></em> 函数。以下是一些范例：
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</p>
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<div class="informalexample">
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<div class="example-contents">
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<div class="phpcode"><code><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$a_bool </span><span style="color: #007700">= </span><span style="color: #0000BB">TRUE</span><span style="color: #007700">; </span><span style="color: #FF8000">// 布尔值 boolean<br /></span><span style="color: #0000BB">$a_str </span><span style="color: #007700">= </span><span style="color: #DD0000">"foo"</span><span style="color: #007700">; </span><span style="color: #FF8000">// 字符串 string<br /></span><span style="color: #0000BB">$a_str2 </span><span style="color: #007700">= </span><span style="color: #DD0000">'foo'</span><span style="color: #007700">; </span><span style="color: #FF8000">// 字符串 string<br /></span><span style="color: #0000BB">$an_int </span><span style="color: #007700">= </span><span style="color: #0000BB">12</span><span style="color: #007700">; </span><span style="color: #FF8000">// 整型 integer<br /><br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">gettype</span><span style="color: #007700">(</span><span style="color: #0000BB">$a_bool</span><span style="color: #007700">); </span><span style="color: #FF8000">// 输出: boolean<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">gettype</span><span style="color: #007700">(</span><span style="color: #0000BB">$a_str</span><span style="color: #007700">); </span><span style="color: #FF8000">// 输出: string<br /><br />// 如果是整型，就加上 4<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">is_int</span><span style="color: #007700">(</span><span style="color: #0000BB">$an_int</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$an_int </span><span style="color: #007700">+= </span><span style="color: #0000BB">4</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #FF8000">// 如果 $bool 是字符串，就打印出来<br />// (啥也没打印出来)<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">is_string</span><span style="color: #007700">(</span><span style="color: #0000BB">$a_bool</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #DD0000">"String: </span><span style="color: #0000BB">$a_bool</span><span style="color: #DD0000">"</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span>
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</span>
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</code></div>
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</div>
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</div>
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</p></blockquote>
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<p class="simpara">
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如果要将一个变量强制转换为某类型，可以对其使用<a href="language.types.type-juggling.html#language.types.typecasting" class="link">强制转换</a>或者 <span class="function"><a href="settype.html" class="function">settype()</a></span> 函数。
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</p>
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<p class="simpara">
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注意变量根据其当时的类型在特定场合下会表现出不同的值。更多信息见<a href="language.types.type-juggling.html" class="link">类型转换的判别</a>。此外，还可以参考
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<a href="types.comparisons.html" class="link">PHP 类型比较表</a>看不同类型相互比较的例子。
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</p>
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</div></div></div></body></html> |