empty

實例

檢查一個變量是否為空。同時檢查該變量是否已設置/聲明：

 <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">// 結果為真，因為$a 是空的</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token keyword">empty</span> <span class="token punctuation">(</span> <span class="token variable">$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">"變量&#39;a&#39; 是空的。<br>"</span> <span class="token punctuation">;</span>  
<span class="token punctuation">}</span>  
  
<span class="token comment">// 結果為真，因為$a 已設置</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token keyword">isset</span> <span class="token punctuation">(</span> <span class="token variable">$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">"變量&#39;a&#39; 已設置"</span> <span class="token punctuation">;</span>  
<span class="token punctuation">}</span>  
<span class="token delimiter important">?></span></span>

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