is_null

實例

檢查變量是否為NULL：

 <span class="token php language-php"><span class="token delimiter important"><?php</span>
<span class="token variable">$a</span> <span class="token operator">=</span> <span class="token number">0</span> <span class="token punctuation">;</span>
<span class="token keyword">echo</span> <span class="token string double-quoted-string">"a is "</span> <span class="token operator">.</span> <span class="token function">is_null</span> <span class="token punctuation">(</span> <span class="token variable">$a</span> <span class="token punctuation">)</span> <span class="token operator">.</span> <span class="token string double-quoted-string">"<br>"</span> <span class="token punctuation">;</span>

<span class="token variable">$b</span> <span class="token operator">=</span> <span class="token constant">null</span> <span class="token punctuation">;</span>
<span class="token keyword">echo</span> <span class="token string double-quoted-string">"b is "</span> <span class="token operator">.</span> <span class="token function">is_null</span> <span class="token punctuation">(</span> <span class="token variable">$b</span> <span class="token punctuation">)</span> <span class="token operator">.</span> <span class="token string double-quoted-string">"<br>"</span> <span class="token punctuation">;</span>

<span class="token variable">$c</span> <span class="token operator">=</span> <span class="token string double-quoted-string">"null"</span> <span class="token punctuation">;</span>
<span class="token keyword">echo</span> <span class="token string double-quoted-string">"c is "</span> <span class="token operator">.</span> <span class="token function">is_null</span> <span class="token punctuation">(</span> <span class="token variable">$c</span> <span class="token punctuation">)</span> <span class="token operator">.</span> <span class="token string double-quoted-string">"<br>"</span> <span class="token punctuation">;</span>

<span class="token variable">$d</span> <span class="token operator">=</span> <span class="token constant">NULL</span> <span class="token punctuation">;</span>
<span class="token keyword">echo</span> <span class="token string double-quoted-string">"d is "</span> <span class="token operator">.</span> <span class="token function">is_null</span> <span class="token punctuation">(</span> <span class="token variable">$d</span> <span class="token punctuation">)</span> <span class="token operator">.</span> <span class="token string double-quoted-string">"<br>"</span> <span class="token punctuation">;</span>
<span class="token delimiter important">?></span></span>

親自試一試

例子解釋：

變量$a 的值為0，不是NULL，所以is_null($a) 返回FALSE。變量$b 和$d 的值都是NULL，所以is_null($b) 和is_null($d) 都返回TRUE。變量$c 的值是一個字符串"null"，不是NULL，所以is_null($c) 返回FALSE。