isset
檢測變量是否已設置並且非null
中文(繁體)
中文(繁體)
檢查變量是否為空。還要檢查變量是否已設置/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">// True because $a is set</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token keyword">isset</span> <span class="token punctuation">(</span> <span class="token variable">$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 'a' is set.<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">// False because $b is NULL</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token keyword">isset</span> <span class="token punctuation">(</span> <span class="token variable">$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">"Variable 'b' is set."</span> <span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token delimiter important">?></span></span>
