PHP中如何使用property_exists 函數檢查對象的類屬性存在情況？

M66 2025-07-18

在PHP中， property_exists函數用於檢查一個對像是否具有某個屬性。它是一個非常有用的工具，尤其是在我們需要動態檢查對象的屬性是否存在時。使用這個函數可以避免直接訪問一個不存在的屬性，從而避免潛在的錯誤或異常。

property_exists函數的基本語法

property_exists函數的語法如下：

 <span><span><span class="hljs-title function_ invoke__">property_exists</span></span><span>(</span><span><span class="hljs-keyword">object</span></span><span> </span><span><span class="hljs-variable">$object</span></span><span>, </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$property</span></span><span>): </span><span><span class="hljs-keyword">bool</span></span><span>
</span></span>

$object ：需要檢查屬性的對象實例。
$property ：要檢查的屬性名稱，必須是一個字符串。

該函數返回一個布爾值：

如果對象具有指定的屬性，則返回true 。
如果對像沒有指定的屬性，則返回false 。

使用property_exists函數的示例

下面通過一個簡單的例子來演示property_exists函數的使用。

 <span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span> </span><span><span class="hljs-title">Person</span></span><span> {
    </span><span><span class="hljs-keyword">public</span></span><span> </span><span><span class="hljs-variable">$name</span></span><span>;
    </span><span><span class="hljs-keyword">private</span></span><span> </span><span><span class="hljs-variable">$age</span></span><span>;

    </span><span><span class="hljs-keyword">public</span></span><span> </span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">__construct</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-variable">$name</span></span></span><span>, </span><span><span class="hljs-variable">$age</span></span><span>) {
        </span><span><span class="hljs-variable language_">$this</span></span><span>-&gt;name = </span><span><span class="hljs-variable">$name</span></span><span>;
        </span><span><span class="hljs-variable language_">$this</span></span><span>-&gt;age = </span><span><span class="hljs-variable">$age</span></span><span>;
    }
}

</span><span><span class="hljs-variable">$person</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title class_">Person</span></span><span>(</span><span><span class="hljs-string">"John"</span></span><span>, </span><span><span class="hljs-number">30</span></span><span>);

</span><span><span class="hljs-comment">// 檢查公共屬性 'name' 是否存在</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">property_exists</span></span><span>(</span><span><span class="hljs-variable">$person</span></span><span>, </span><span><span class="hljs-string">'name'</span></span><span>)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'name' 存在。\n"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'name' 不存在。\n"</span></span><span>;
}

</span><span><span class="hljs-comment">// 檢查私有屬性 'age' 是否存在</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">property_exists</span></span><span>(</span><span><span class="hljs-variable">$person</span></span><span>, </span><span><span class="hljs-string">'age'</span></span><span>)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'age' 存在。\n"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'age' 不存在。\n"</span></span><span>;
}

</span><span><span class="hljs-comment">// 檢查不存在的屬性 'address'</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">property_exists</span></span><span>(</span><span><span class="hljs-variable">$person</span></span><span>, </span><span><span class="hljs-string">'address'</span></span><span>)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'address' 存在。\n"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'address' 不存在。\n"</span></span><span>;
}
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

輸出結果如下：

 <span><span>屬性 </span><span><span class="hljs-string">'name'</span></span><span> 存在。
屬性 </span><span><span class="hljs-string">'age'</span></span><span> 存在。
屬性 </span><span><span class="hljs-string">'address'</span></span><span> 不存在。
</span></span>

property_exists的工作原理

需要注意的是， property_exists函數不僅檢查對象實例是否具有指定的屬性，還會檢查該屬性的可見性（public、protected、private）。這意味著：

它會返回true ，即使該屬性是私有的或受保護的。
但是，它不會檢查屬性的值是否被初始化。

例如，如果一個私有屬性在構造函數中沒有被初始化， property_exists仍然會返回true ，因為它只是檢查屬性是否存在，而不關心屬性的實際值。

結合其他函數使用

有時，我們可能會結合property_exists和isset或empty等函數使用，以確保在訪問某個屬性之前，屬性不僅存在，還已經被初始化並且不為空。示例如下：

 <span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span> </span><span><span class="hljs-title">Person</span></span><span> {
    </span><span><span class="hljs-keyword">public</span></span><span> </span><span><span class="hljs-variable">$name</span></span><span>;
    </span><span><span class="hljs-keyword">private</span></span><span> </span><span><span class="hljs-variable">$age</span></span><span>;

    </span><span><span class="hljs-keyword">public</span></span><span> </span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">__construct</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-variable">$name</span></span></span><span>) {
        </span><span><span class="hljs-variable language_">$this</span></span><span>-&gt;name = </span><span><span class="hljs-variable">$name</span></span><span>;
    }
}

</span><span><span class="hljs-variable">$person</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title class_">Person</span></span><span>(</span><span><span class="hljs-string">"John"</span></span><span>);

</span><span><span class="hljs-comment">// 檢查 'age' 屬性是否存在並且已初始化</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">property_exists</span></span><span>(</span><span><span class="hljs-variable">$person</span></span><span>, </span><span><span class="hljs-string">'age'</span></span><span>) &amp;&amp; </span><span><span class="hljs-keyword">isset</span></span><span>(</span><span><span class="hljs-variable">$person</span></span><span>-&gt;age)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'age' 存在並且已初始化。\n"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'age' 不存在或未初始化。\n"</span></span><span>;
}

</span><span><span class="hljs-comment">// 檢查 'name' 屬性是否存在並且已初始化</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">property_exists</span></span><span>(</span><span><span class="hljs-variable">$person</span></span><span>, </span><span><span class="hljs-string">'name'</span></span><span>) &amp;&amp; </span><span><span class="hljs-keyword">isset</span></span><span>(</span><span><span class="hljs-variable">$person</span></span><span>-&gt;name)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"屬性 'name' 存在並且已初始化。\n"</span></span><span>;
}
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

總結

property_exists是PHP中的一個非常實用的函數，能夠幫助我們檢查對象的某個屬性是否存在。與直接訪問屬性的方式不同，使用property_exists可以有效避免因訪問不存在的屬性而引發錯誤。通過這個函數，我們可以更安全地處理對象屬性的存在與否，尤其是在處理動態生成對像或數據不確定的情況時。