empty

名称:empty

分类:变量处理

所属语言:php

一句话介绍:检查变量是否为空。

实例

检查一个变量是否为空。同时检查该变量是否已设置/声明：

<span class="token php language-php"><span class="token delimiter important"><?php</span>  
<span class="token variable">$a</span> <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>  
  
<span class="token comment">// 结果为真，因为 $a 是空的  </span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">empty</span><span class="token punctuation">(</span><span class="token variable">$a</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>  
  <span class="token keyword">echo</span> <span class="token string double-quoted-string">"变量 'a' 是空的。<br>"</span><span class="token punctuation">;</span>  
<span class="token punctuation">}</span>  
  
<span class="token comment">// 结果为真，因为 $a 已设置  </span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">isset</span><span class="token punctuation">(</span><span class="token variable">$a</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>  
  <span class="token keyword">echo</span> <span class="token string double-quoted-string">"变量 'a' 已设置"</span><span class="token punctuation">;</span>  
<span class="token punctuation">}</span>  
<span class="token delimiter important">?></span></span>

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