PHP ctype_upper 函數遇到非字母字符時的行為分析

gitbox 2025-09-02
<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，僅作佔位和分隔作用</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"PHP 函數行為分析示例\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">/**
 * PHP ctype_upper 函數遇到非字母字符時的行為分析
 *
 * ctype_upper 是 PHP 中用來檢測字符串中所有字母是否都是大寫字母的函數。
 * 函數原型如下：
 * bool ctype_upper(string $text)
 *
 * 函數返回 true 當且僅當字符串非空且所有字母都是大寫；如果字符串包含非字母字符，則這些字符不會影響結果，但空字符串會返回 false。
 *
 * 行為分析：
 */</span>

</span><span><span class="hljs-comment">// 示例 1：純大寫字母</span></span><span>
</span><span><span class="hljs-variable">$str1</span></span><span> = </span><span><span class="hljs-string">"HELLO"</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">ctype_upper</span></span><span>(</span><span><span class="hljs-variable">$str1</span></span><span>)); </span><span><span class="hljs-comment">// 輸出: bool(true)</span></span><span>

</span><span><span class="hljs-comment">// 示例 2：包含小寫字母</span></span><span>
</span><span><span class="hljs-variable">$str2</span></span><span> = </span><span><span class="hljs-string">"Hello"</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">ctype_upper</span></span><span>(</span><span><span class="hljs-variable">$str2</span></span><span>)); </span><span><span class="hljs-comment">// 輸出: bool(false)</span></span><span>

</span><span><span class="hljs-comment">// 示例 3：包含數字</span></span><span>
</span><span><span class="hljs-variable">$str3</span></span><span> = </span><span><span class="hljs-string">"HELLO123"</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">ctype_upper</span></span><span>(</span><span><span class="hljs-variable">$str3</span></span><span>)); </span><span><span class="hljs-comment">// 輸出: bool(true)  非字母字符不影響判斷</span></span><span>

</span><span><span class="hljs-comment">// 示例 4：包含符號</span></span><span>
</span><span><span class="hljs-variable">$str4</span></span><span> = </span><span><span class="hljs-string">"HELLO!"</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">ctype_upper</span></span><span>(</span><span><span class="hljs-variable">$str4</span></span><span>)); </span><span><span class="hljs-comment">// 輸出: bool(true)  非字母字符不影響判斷</span></span><span>

</span><span><span class="hljs-comment">// 示例 5：空字符串</span></span><span>
</span><span><span class="hljs-variable">$str5</span></span><span> = </span><span><span class="hljs-string">""</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">ctype_upper</span></span><span>(</span><span><span class="hljs-variable">$str5</span></span><span>)); </span><span><span class="hljs-comment">// 輸出: bool(false)  空字符串返回 false</span></span><span>

<span class="hljs-comment">/**
 * 關鍵點總結：
 * 1. ctype_upper 只檢查字母字符，大寫字母返回 true。
 * 2. 非字母字符（如數字、標點符號、空格）不會導致返回 false。
 * 3. 空字符串始終返回 false。
 * 4. 如果字符串包含任何小寫字母，則返回 false。
 *
 * 使用場景提示：
 * 當需要嚴格判斷字符串是否完全由大寫字母組成時，可以直接使用 ctype_upper。
 * 如果希望忽略非字母字符的影響，它也可以直接使用而無需額外處理。
 */</span>
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>
ctype_upper