is_null

Beispiel

Überprüfen Sie, ob die Variable null ist:

 <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 ist"</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 ist"</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 ist"</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 ist"</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>

Probieren Sie es selbst aus

Beispiel Erklärung:

Der Wert der Variablen $ A beträgt 0, nicht null, so ist is_null ($ a) falsch zurück. Die Werte der Variablen $ B und $ D sind null, sodass sowohl is_null ($ b) als auch is_null ($ d) true zurückgeben. Der Wert der Variablen $ C ist eine Zeichenfolge "NULL", nicht null, so dass is_null ($ c) false zurückgibt.