能用PHP的octdec和decoct函数实现八进制与十进制的双向转换吗？

gitbox 2025-09-12

—— 和正文无关的内容分隔线 ——

结论先说：可以。octdec() 用于把八进制字符串 → 十进制整数，decoct() 用于把十进制整数 → 八进制字符串。两者配合即可实现双向转换。下面把用法、易错点与进阶方案一次讲清。

1. 基本用法

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 八进制 → 十进制</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">octdec</span></span><span>(</span><span><span class="hljs-string">'17'</span></span><span>);   </span><span><span class="hljs-comment">// 15</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> PHP_EOL;
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">octdec</span></span><span>(</span><span><span class="hljs-string">'011'</span></span><span>);  </span><span><span class="hljs-comment">// 9（字符串里的前导 0 不会改变含义，它仍按八进制解析）</span></span><span>

</span><span><span class="hljs-comment">// 十进制 → 八进制</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">decoct</span></span><span>(</span><span><span class="hljs-number">15</span></span><span>);     </span><span><span class="hljs-comment">// "17"</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> PHP_EOL;
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">decoct</span></span><span>(</span><span><span class="hljs-number">9</span></span><span>);      </span><span><span class="hljs-comment">// "11"</span></span><span>
</span></span>

要点：

octdec(string $octal): int —— 参数是字符串，返回十进制整数。
decoct(int $decimal): string —— 参数是整数，返回八进制的字符串。

2. 常见陷阱与边界

(1) 非法字符

八进制只允许 0–7。传入如 8、9 或非数字字符会被忽略到第一个非法处之后，结果容易与你的预期不符。先校验再转换最稳妥。

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">isValidOctal</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$s</span></span><span>): </span><span><span class="hljs-title">bool</span></span><span> {
    </span><span><span class="hljs-comment">// 允许前导 0；至少一个八进制数字</span></span><span>
    </span><span><span class="hljs-keyword">return</span></span><span> (</span><span><span class="hljs-keyword">bool</span></span><span>)</span><span><span class="hljs-title function_ invoke__">preg_match</span></span><span>(</span><span><span class="hljs-string">'/^[0-7]+$/'</span></span><span>, </span><span><span class="hljs-variable">$s</span></span><span>);
}

</span><span><span class="hljs-variable">$input</span></span><span> = </span><span><span class="hljs-string">'128'</span></span><span>; </span><span><span class="hljs-comment">// 非法</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">isValidOctal</span></span><span>(</span><span><span class="hljs-variable">$input</span></span><span>)) {
    </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">"不是合法的八进制数：<span class="hljs-subst">{$input}</span></span></span><span>");
}
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">octdec</span></span><span>(</span><span><span class="hljs-variable">$input</span></span><span>);
</span></span>

(2) 前导 0 与代码里的“八进制字面量”

字符串 "011" 只是文本，octdec("011") 会按八进制解析为 9。
PHP 代码里的整数字面量 若写成 011，这是八进制字面量（等于十进制 9）。建议避免在源码中使用前导 0 的整数字面量，以免阅读混淆；需要八进制时更清晰的做法是使用字符串配合 octdec()。

(3) 负数与位宽

decoct() 的参数是整数。对负数时，它会按实现平台的位宽（通常 64 位）以二进制补码形式参与运算并给出一个看起来“很长”的八进制表示，这通常不是你要的结果。如无特别需求，请只处理非负整数。

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">decoct</span></span><span>(-</span><span><span class="hljs-number">10</span></span><span>); </span><span><span class="hljs-comment">// 依平台而异，通常是很长的一串</span></span><span>
</span></span>

(4) 大整数

在 64 位 PHP 上，int 最大约为 9.22e18。decoct() 受此限制。
若需要处理超大十进制数（超过 int 范围）的转换，考虑：
- 使用 gmp_* （如 gmp_init + gmp_strval($n, 8)）；
- 或使用 bc/自写大数算法。
八进制→十进制时，octdec() 返回 int，同样受限；超出时请改用 gmp/bc 方案。

3. 实用封装：稳健的双向转换

八进制字符串 → 十进制（返回 int）

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">octalToDecimal</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$oct</span></span><span>): </span><span><span class="hljs-title">int</span></span><span> {
    </span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">preg_match</span></span><span>(</span><span><span class="hljs-string">'/^[0-7]+$/'</span></span><span>, </span><span><span class="hljs-variable">$oct</span></span><span>)) {
        </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">"非法八进制：<span class="hljs-subst">$oct</span></span></span><span>");
    }
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">octdec</span></span><span>(</span><span><span class="hljs-variable">$oct</span></span><span>);
}
</span></span>

十进制（非负 int）→ 八进制字符串

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">decimalToOctal</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">int</span></span></span><span> </span><span><span class="hljs-variable">$dec</span></span><span>): </span><span><span class="hljs-title">string</span></span><span> {
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$dec</span></span><span> &lt; </span><span><span class="hljs-number">0</span></span><span>) {
        </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">"只支持非负整数"</span></span><span>);
    }
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">decoct</span></span><span>(</span><span><span class="hljs-variable">$dec</span></span><span>);
}
</span></span>

进阶：用 GMP 支持超大数

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">octalToDecimalBig</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$oct</span></span><span>): </span><span><span class="hljs-title">string</span></span><span> {
    </span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">preg_match</span></span><span>(</span><span><span class="hljs-string">'/^[0-7]+$/'</span></span><span>, </span><span><span class="hljs-variable">$oct</span></span><span>)) {
        </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">"非法八进制：<span class="hljs-subst">$oct</span></span></span><span>");
    }
    </span><span><span class="hljs-variable">$g</span></span><span> = </span><span><span class="hljs-title function_ invoke__">gmp_init</span></span><span>(</span><span><span class="hljs-variable">$oct</span></span><span>, </span><span><span class="hljs-number">8</span></span><span>);
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">gmp_strval</span></span><span>(</span><span><span class="hljs-variable">$g</span></span><span>, </span><span><span class="hljs-number">10</span></span><span>); </span><span><span class="hljs-comment">// 返回十进制“字符串”</span></span><span>
}

</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">decimalToOctalBig</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$dec</span></span><span>): </span><span><span class="hljs-title">string</span></span><span> {
    </span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">preg_match</span></span><span>(</span><span><span class="hljs-string">'/^[0-9]+$/'</span></span><span>, </span><span><span class="hljs-variable">$dec</span></span><span>)) {
        </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">"非法十进制：<span class="hljs-subst">$dec</span></span></span><span>");
    }
    </span><span><span class="hljs-variable">$g</span></span><span> = </span><span><span class="hljs-title function_ invoke__">gmp_init</span></span><span>(</span><span><span class="hljs-variable">$dec</span></span><span>, </span><span><span class="hljs-number">10</span></span><span>);
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">gmp_strval</span></span><span>(</span><span><span class="hljs-variable">$g</span></span><span>, </span><span><span class="hljs-number">8</span></span><span>);
}
</span></span>

提示：GMP 扩展需在环境中启用；如果不能使用 GMP，可用 bc 或纯 PHP 实现逐位进制转换。

4. 与 base_convert() 的对比

base_convert(string $num, int $from, int $to) 也能实现进制转换，例如：

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">base_convert</span></span><span>(</span><span><span class="hljs-string">'17'</span></span><span>, </span><span><span class="hljs-number">8</span></span><span>, </span><span><span class="hljs-number">10</span></span><span>); </span><span><span class="hljs-comment">// "15"</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">base_convert</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">8</span></span><span>); </span><span><span class="hljs-comment">// "17"</span></span><span>
</span></span>

区别与取舍：

base_convert() 入参/出参都是字符串，更接近“文本进制转换”的语义；
octdec()/decoct() 更贴近 “八进制?十进制”的专用 API，语义明确，且 octdec() 直接返回 int，用起来顺手；
面对超大整数时，base_convert() 在部分场景会受实现与精度限制；要绝对稳妥，仍建议用 gmp/bc。

5. 小结

答案：可以。 用 octdec()（八进制字符串→十进制 int）与 decoct()（十进制 int→八进制字符串）即可实现双向转换。
生产实践里请注意：输入校验、负数处理、整数字面量前导 0 的歧义、以及大整数的溢出问题。需要大数支持时，选择 gmp/bc 等方案更稳健。