isset
检测变量是否已设置并且非 null
简体中文
简体中文
检查变量是否为空。还要检查变量是否已设置/声明：
<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>
is_numeric
is_integer
serialize
debug_zval_dump
is_long
empty
get_debug_type
is_real
