iconv_substr 截取字符串时，如何防止发生 "字符截断" 错误？

M66 2025-07-25

三、导致“字符截断”错误的原因

：默认编码可能不是你字符串的实际编码，导致截取字节数错误。
截取长度超出实际字符数：截取位置超出字符串长度时，可能报错。
字符串本身编码不一致或损坏。

四、如何防止“字符截断”错误？

明确指定编码

<span><span><span class="hljs-variable">$encoding</span></span><span> = </span><span><span class="hljs-string">'UTF-8'</span></span><span>;
</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">iconv_substr</span></span><span>(</span><span><span class="hljs-variable">$str</span></span><span>, </span><span><span class="hljs-variable">$offset</span></span><span>, </span><span><span class="hljs-variable">$length</span></span><span>, </span><span><span class="hljs-variable">$encoding</span></span><span>);
</span></span>

保证截取的长度和偏移都是基于字符，不是字节

iconv_substr 的 $offset 和 $length 是字符计数，不是字节，但字符串必须是指定的编码。

提前检测字符串长度

使用 iconv_strlen 来确定字符串长度，避免越界：

<span><span><span class="hljs-variable">$length</span></span><span> = </span><span><span class="hljs-title function_ invoke__">iconv_strlen</span></span><span>(</span><span><span class="hljs-variable">$str</span></span><span>, </span><span><span class="hljs-variable">$encoding</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$offset</span></span><span> &gt; </span><span><span class="hljs-variable">$length</span></span><span>) {
    </span><span><span class="hljs-comment">// 处理偏移越界</span></span><span>
}
</span></span>

错误处理

iconv_substr 出错时可能返回 false，要做好判断：

<span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">iconv_substr</span></span><span>(</span><span><span class="hljs-variable">$str</span></span><span>, </span><span><span class="hljs-variable">$offset</span></span><span>, </span><span><span class="hljs-variable">$length</span></span><span>, </span><span><span class="hljs-variable">$encoding</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$result</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
    </span><span><span class="hljs-comment">// 处理截取失败，避免程序异常</span></span><span>
}
</span></span>

使用 mbstring 函数作为替代

mb_substr 也是多字节安全的字符串截取函数，常用于替代 iconv_substr：

<span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">mb_substr</span></span><span>(</span><span><span class="hljs-variable">$str</span></span><span>, </span><span><span class="hljs-variable">$offset</span></span><span>, </span><span><span class="hljs-variable">$length</span></span><span>, </span><span><span class="hljs-variable">$encoding</span></span><span>);
</span></span>

五、示例代码

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-variable">$str</span></span><span> = </span><span><span class="hljs-string">"这是一个测试字符串，用于演示 iconv_substr 的用法。"</span></span><span>;
</span><span><span class="hljs-variable">$encoding</span></span><span> = </span><span><span class="hljs-string">'UTF-8'</span></span><span>;
</span><span><span class="hljs-variable">$offset</span></span><span> = </span><span><span class="hljs-number">3</span></span><span>;
</span><span><span class="hljs-variable">$length</span></span><span> = </span><span><span class="hljs-number">5</span></span><span>;

</span><span><span class="hljs-variable">$totalLength</span></span><span> = </span><span><span class="hljs-title function_ invoke__">iconv_strlen</span></span><span>(</span><span><span class="hljs-variable">$str</span></span><span>, </span><span><span class="hljs-variable">$encoding</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$offset</span></span><span> &gt; </span><span><span class="hljs-variable">$totalLength</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"截取起始位置超过字符串长度。"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-variable">$substr</span></span><span> = </span><span><span class="hljs-title function_ invoke__">iconv_substr</span></span><span>(</span><span><span class="hljs-variable">$str</span></span><span>, </span><span><span class="hljs-variable">$offset</span></span><span>, </span><span><span class="hljs-variable">$length</span></span><span>, </span><span><span class="hljs-variable">$encoding</span></span><span>);
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$substr</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"字符串截取失败，可能存在编码问题。"</span></span><span>;
    } </span><span><span class="hljs-keyword">else</span></span><span> {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"截取结果："</span></span><span> . </span><span><span class="hljs-variable">$substr</span></span><span>;
    }
}
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

iconv_substr