遇到類型不匹配？看看mysqli_result::$lengths 在使用時應該注意哪些類型問題

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 這部分代碼與正文內容無關，僅作示例用途</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"開始執行腳本...\n"</span></span><span>;
</span><span><span class="hljs-meta">?&gt;</span></span><span>

&lt;hr&gt;

</span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/*
遇到類型不匹配？看看 mysqli_result::$lengths 在使用時應該注意哪些類型問題
*/</span>

<span class="hljs-comment">/**
 * mysqli_result::$lengths 是一個數組，包含了結果集中每個字段對應數據的長度。
 * 使用時需要注意，這些長度值的類型和使用場景。
 */</span>

</span><span><span class="hljs-variable">$mysqli</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">mysqli</span></span><span>(</span><span><span class="hljs-string">"localhost"</span></span><span>, </span><span><span class="hljs-string">"user"</span></span><span>, </span><span><span class="hljs-string">"password"</span></span><span>, </span><span><span class="hljs-string">"testdb"</span></span><span>);

</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;connect_error) {
    </span><span><span class="hljs-keyword">die</span></span><span>(</span><span><span class="hljs-string">"連接失敗: "</span></span><span> . </span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;connect_error);
}

</span><span><span class="hljs-variable">$sql</span></span><span> = </span><span><span class="hljs-string">"SELECT id, name, description FROM products"</span></span><span>;
</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">query</span></span><span>(</span><span><span class="hljs-variable">$sql</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-keyword">instanceof</span></span><span> mysqli_result) {
    </span><span><span class="hljs-comment">// $lengths 是一個整數數組，元素對應每個字段的字節長度</span></span><span>
    </span><span><span class="hljs-variable">$lengths</span></span><span> = </span><span><span class="hljs-variable">$result</span></span><span>-&gt;lengths;

    </span><span><span class="hljs-comment">// 示例：獲取長度數組並打印</span></span><span>
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"字段長度數組類型: "</span></span><span> . </span><span><span class="hljs-title function_ invoke__">gettype</span></span><span>(</span><span><span class="hljs-variable">$lengths</span></span><span>) . </span><span><span class="hljs-string">"\n"</span></span><span>;
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"字段長度內容：\n"</span></span><span>;
    </span><span><span class="hljs-title function_ invoke__">print_r</span></span><span>(</span><span><span class="hljs-variable">$lengths</span></span><span>);

    <span class="hljs-comment">/*
     * 類型問題要點說明：
     * 1. $lengths 是一個數組，且每個元素是整型（int）。
     * 2. 這些長度是字節數，注意與字符串長度函數 strlen 可能得到的字符數不同，尤其是多字節字符。
     * 3. $lengths 數組只在使用 mysqli::store_result 或者默認緩衝結果時有效，使用 mysqli_use_result 時不可用。
     * 4. 訪問前務必確認 $result 是有效的 mysqli_result 對象，否則 $lengths 不存在或報錯。
     */</span>

    </span><span><span class="hljs-comment">// 進一步示例：使用長度信息處理數據</span></span><span>
    </span><span><span class="hljs-keyword">while</span></span><span> (</span><span><span class="hljs-variable">$row</span></span><span> = </span><span><span class="hljs-variable">$result</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">fetch_assoc</span></span><span>()) {
        </span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$row</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$field</span></span><span> =&gt; </span><span><span class="hljs-variable">$value</span></span><span>) {
            </span><span><span class="hljs-variable">$idx</span></span><span> = </span><span><span class="hljs-title function_ invoke__">array_search</span></span><span>(</span><span><span class="hljs-variable">$field</span></span><span>, </span><span><span class="hljs-title function_ invoke__">array_keys</span></span><span>(</span><span><span class="hljs-variable">$row</span></span><span>));
            </span><span><span class="hljs-variable">$len</span></span><span> = </span><span><span class="hljs-variable">$lengths</span></span><span>[</span><span><span class="hljs-variable">$idx</span></span><span>] ?? </span><span><span class="hljs-literal">null</span></span><span>;

            </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"字段 '<span class="hljs-subst">{$field}</span></span></span><span>' 的值長度（位元組）為：</span><span><span class="hljs-subst">{$len}</span></span><span>\n";
            </span><span><span class="hljs-comment">// 注意這裡的 $len 是位元組长度，不一定等於字符串字符數</span></span><span>
            </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"字符串字符數："</span></span><span> . </span><span><span class="hljs-title function_ invoke__">mb_strlen</span></span><span>(</span><span><span class="hljs-variable">$value</span></span><span>, </span><span><span class="hljs-string">'UTF-8'</span></span><span>) . </span><span><span class="hljs-string">"\n"</span></span><span>;
        }
    }

    </span><span><span class="hljs-variable">$result</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">free</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">"查詢失敗或無結果。\n"</span></span><span>;
}

</span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">close</span></span><span>();
</span><span><span class="hljs-meta">?&gt;</span></span><span>

&lt;hr&gt;

</span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 這部分代碼與正文內容無關，僅作示例用途</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"腳本執行結束。\n"</span></span><span>;
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

• 相關標籤:

  mysqli_result