is_null

例

変数がnullであるかどうかを確認します。

 <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">エコー</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">エコー</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>

自分で試してみてください

例説明：

変数$ aの値は0であり、nullではなく、is_null（$ a）がfalseを返します。変数$ bと$ dの値はnullであるため、is_null（$ b）とis_null（$ d）の両方がtrueを返します。変数$ cの値は文字列「null」であり、nullではなく、is_null（$ c）がfalseを返します。