base_convert() 函數中處理負數進制轉換時，有哪些注意事項？

gitbox 2025-08-15
<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 這部分代碼與文章內容無關，僅作為前置代碼示例</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"開始執行 PHP 腳本...\n"</span></span><span>;
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</span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/*
 * base_convert() 函數中處理負數進制轉換時，有哪些注意事項？
 *
 * base_convert() 是 PHP 內置的一個函數，用於在不同的進制之間轉換數字字符串。
 * 它的函數簽名是：string base_convert(string $number, int $from_base, int $to_base)
 *
 * 但在實際使用中，base_convert() 並不支持直接處理負數。
 * 下面將詳細說明關於負數和進制轉換時需要注意的幾個關鍵點。
 */</span>

</span><span><span class="hljs-comment">// 1. base_convert() 不支持負數輸入</span></span><span>
</span><span><span class="hljs-comment">// base_convert() 接收的 $number 參數是字符串形式的數字，且該數字只能是非負整數。</span></span><span>
</span><span><span class="hljs-comment">// 如果傳入帶負號的字符串（如 "-15"），函數會將負號當成非法字符忽略，導致結果不正確。</span></span><span>

</span><span><span class="hljs-comment">// 示例</span></span><span>
</span><span><span class="hljs-variable">$negativeNumber</span></span><span> = </span><span><span class="hljs-string">"-15"</span></span><span>;
</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">base_convert</span></span><span>(</span><span><span class="hljs-variable">$negativeNumber</span></span><span>, </span><span><span class="hljs-number">10</span></span><span>, </span><span><span class="hljs-number">2</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"轉換結果（輸入帶負號）: <span class="hljs-subst">$result</span></span></span><span>\n"; 
</span><span><span class="hljs-comment">// 輸出結果會忽略負號，等同於轉換“15”，並不是期望的負數二進製表示。</span></span><span>

</span><span><span class="hljs-comment">// 2. 處理負數的常用方法</span></span><span>
</span><span><span class="hljs-comment">// 由於 base_convert() 不支持負數轉換，通常的做法是先檢測數字的正負號，</span></span><span>
</span><span><span class="hljs-comment">// 然後對絕對值進行進制轉換，最後再手動添加負號。</span></span><span>

</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">base_convert_negative</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$number</span></span><span>, </span><span><span class="hljs-keyword">int</span></span><span> </span><span><span class="hljs-variable">$from_base</span></span><span>, </span><span><span class="hljs-keyword">int</span></span><span> </span><span><span class="hljs-variable">$to_base</span></span><span>): </span><span><span class="hljs-title">string</span></span><span> {
    </span><span><span class="hljs-variable">$isNegative</span></span><span> = </span><span><span class="hljs-literal">false</span></span><span>;
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">strlen</span></span><span>(</span><span><span class="hljs-variable">$number</span></span><span>) &gt; </span><span><span class="hljs-number">0</span></span><span> &amp;&amp; </span><span><span class="hljs-variable">$number</span></span><span>[</span><span><span class="hljs-number">0</span></span><span>] === </span><span><span class="hljs-string">'-'</span></span><span>) {
        </span><span><span class="hljs-variable">$isNegative</span></span><span> = </span><span><span class="hljs-literal">true</span></span><span>;
        </span><span><span class="hljs-variable">$number</span></span><span> = </span><span><span class="hljs-title function_ invoke__">substr</span></span><span>(</span><span><span class="hljs-variable">$number</span></span><span>, </span><span><span class="hljs-number">1</span></span><span>);
    }
    </span><span><span class="hljs-variable">$converted</span></span><span> = </span><span><span class="hljs-title function_ invoke__">base_convert</span></span><span>(</span><span><span class="hljs-variable">$number</span></span><span>, </span><span><span class="hljs-variable">$from_base</span></span><span>, </span><span><span class="hljs-variable">$to_base</span></span><span>);
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-variable">$isNegative</span></span><span> ? </span><span><span class="hljs-string">'-'</span></span><span> . </span><span><span class="hljs-variable">$converted</span></span><span> : </span><span><span class="hljs-variable">$converted</span></span><span>;
}

</span><span><span class="hljs-comment">// 測試</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">base_convert_negative</span></span><span>(</span><span><span class="hljs-string">"-15"</span></span><span>, </span><span><span class="hljs-number">10</span></span><span>, </span><span><span class="hljs-number">2</span></span><span>) . </span><span><span class="hljs-string">"\n"</span></span><span>;  </span><span><span class="hljs-comment">// 輸出：-1111</span></span><span>

</span><span><span class="hljs-comment">// 3. 進制轉換的範圍限制</span></span><span>
</span><span><span class="hljs-comment">// base_convert() 支持的進制範圍是 2 到 36。</span></span><span>
</span><span><span class="hljs-comment">// 如果試圖轉換超出這個範圍的進制，函數會返回空字符串。</span></span><span>
</span><span><span class="hljs-comment">// 所以在處理負數時，也需要保證傳入的進制合法。</span></span><span>

</span><span><span class="hljs-comment">// 4. 負數的進製表現形式</span></span><span>
</span><span><span class="hljs-comment">// 在某些場景中，可能希望用補碼形式表示負數的二進制。</span></span><span>
</span><span><span class="hljs-comment">// 但 base_convert() 只是簡單轉換數值，不支持補碼或有符號數的轉換。</span></span><span>
</span><span><span class="hljs-comment">// 如果需要補碼表示，必須自行處理位運算和格式化。</span></span><span>

</span><span><span class="hljs-comment">// 5. 總結</span></span><span>
</span><span><span class="hljs-comment">// - base_convert() 不支持直接轉換帶負號的數字。</span></span><span>
</span><span><span class="hljs-comment">// - 需要手動分離負號，轉換絕對值，再加回負號。</span></span><span>
</span><span><span class="hljs-comment">// - 進制必須在 2 到 36 之間。</span></span><span>
</span><span><span class="hljs-comment">// - 補碼或其他負數二進製表示需自行實現。</span></span><span>

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base_convert