isset

Exemple

Vérifiez si la variable est vide. Vérifiez également si la variable est définie / déclarée:

 <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">// vrai parce que $ a est défini</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">"variable &#39;a&#39; est défini. <br>"</span> <span class="token punctuation">;</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 comment">// faux parce que $ b est nul</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">$ b</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">"La variable &#39;b&#39; est définie."</span> <span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token delimiter important">?></span></span>

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