iconv_substr 截取字符串時，如何防止發生"字符截斷" 錯誤？

M66 2025-07-25

三、導致“字符截斷”錯誤的原因

：默認編碼可能不是你字符串的實際編碼，導致截取字節數錯誤。
截取長度超出實際字符數：截取位置超出字符串長度時，可能報錯。
字符串本身編碼不一致或損壞。

四、如何防止“字符截斷”錯誤？

明確指定編碼

<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>

保證截取的長度和偏移都是基於字符，不是字節

iconv_substr的$offset和$length是字符計數，不是字節，但字符串必須是指定的編碼。

提前檢測字符串長度

使用iconv_strlen來確定字符串長度，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">// 處理偏移越界</span></span><span>
}
</span></span>

錯誤處理

iconv_substr出錯時可能返回false ，要做好判斷：

 <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">// 處理截取失敗，避免程序異常</span></span><span>
}
</span></span>

使用mbstring 函數作為替代

mb_substr也是多字節安全的字符串截取函數，常用於替代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、示例代碼

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-variable">$str</span></span><span> = </span><span><span class="hljs-string">"這是一個測試字符串，用於演示 iconv_substr 的用法。"</span></span><span>;
</span><span><span class="hljs-variable">$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">$totalLength</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"截取起始位置超過字符串長度。"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-variable">$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">$substr</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"字符串截取失敗，可能存在編碼問題。"</span></span><span>;
    } </span><span><span class="hljs-keyword">else</span></span><span> {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"截取結果："</span></span><span> . </span><span><span class="hljs-variable">$substr</span></span><span>;
    }
}
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

iconv_substr