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36 lines
2.7 KiB
HTML
36 lines
2.7 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>检测变量是否为 NULL</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.is-null" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">is_null</h1>
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<p class="verinfo">(PHP 4 >= 4.0.4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">is_null</span> — <span class="dc-title">
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检测变量是否为 <strong><code>NULL</code></strong>
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</span></p>
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</div>
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<div class="refsect1 unknown-unknown-seealsq" id="refsect1-function.is-null-unknown-unknown-seealsq">
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<h3 class="title">描述</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>is_null</strong></span>
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( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$var</code></span>
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) : <span class="type">bool</span></div>
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<p class="para rdfs-comment">
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如果 <code class="parameter">var</code> 是 <span class="type"><a href="language.types.null.html" class="type null">null</a></span> 则返回 <strong><code>TRUE</code></strong>，否则返回 <strong><code>FALSE</code></strong>。
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</p>
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<p class="para">
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查看 <a href="language.types.null.html#language.types.null.syntax" class="link"><strong><code>NULL</code></strong></a> 类型获知变量什么时候被认为是 <strong><code>NULL</code></strong>，而什么时候不是。
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</p>
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<p class="para">
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参见
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<a href="language.types.null.html#language.types.null.syntax" class="link"><strong><code>NULL</code></strong></a>、<span class="function"><a href="is_bool.html" class="function">is_bool()</a></span>、<span class="function"><a href="is_numeric.html" class="function">is_numeric()</a></span>、<span class="function"><a href="is_float.html" class="function">is_float()</a></span>、<span class="function"><a href="is_int.html" class="function">is_int()</a></span>、<span class="function"><a href="is_string.html" class="function">is_string()</a></span>、<span class="function"><a href="is_object.html" class="function">is_object()</a></span>、<span class="function"><a href="is_array.html" class="function">is_array()</a></span>、<span class="function"><a href="is_integer.html" class="function">is_integer()</a></span>
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和 <span class="function"><a href="is_real.html" class="function">is_real()</a></span>。
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</p>
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</div>
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</div></div></div></body></html> |