怎样利用 chr() 函数生成带有特殊字符的字符串？

gitbox 2025-09-23

在 PHP 中，chr() 是一个非常基础但常用的函数：它接受一个整数（0–255）并返回对应的单字节字符。例如 chr(65) 返回 "A"。不过在处理“特殊字符”——比如控制字符、二进制字节序列、或多字节（UTF-8）字符（例如中文、表情）时，需要理解 chr() 的局限并配合其他方法来生成期望的字符串。

下面分几个场景说明常见做法与注意事项，并给出可直接复制运行的示例。

1) 生成 ASCII / 控制字符（单字节）

chr() 最擅长的就是生成单字节字符：可用于生成换行、制表符、不可见控制字符或者任意 0–255 的字节值。

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 大写 A</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">65</span></span><span>); </span><span><span class="hljs-comment">// 输出 A</span></span><span>

</span><span><span class="hljs-comment">// 换行（LF）</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"line1"</span></span><span> . </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">10</span></span><span>) . </span><span><span class="hljs-string">"line2"</span></span><span>;

</span><span><span class="hljs-comment">// 制表符（TAB）</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"col1"</span></span><span> . </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">9</span></span><span>) . </span><span><span class="hljs-string">"col2"</span></span><span>;

</span><span><span class="hljs-comment">// 生成二进制数据片段</span></span><span>
</span><span><span class="hljs-variable">$bytes</span></span><span> = </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x00</span></span><span>) . </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0xFF</span></span><span>) . </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x7A</span></span><span>);
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-variable">$bytes</span></span><span>); </span><span><span class="hljs-comment">// string(3) "\x00\xFFz"</span></span><span>
</span></span>

提示：当你处理二进制协议、文件头或网络包时，chr() 非常方便来构造任意字节。

2) 一次生成多个字节：使用 pack() 或拼接 chr()

如果要一次性构造多个连续的字节，pack() 比大量拼接 chr() 更简洁且性能好一些。

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 用 pack 生成三个字节：0x01 0x02 0x03</span></span><span>
</span><span><span class="hljs-variable">$bin</span></span><span> = </span><span><span class="hljs-title function_ invoke__">pack</span></span><span>(</span><span><span class="hljs-string">'C*'</span></span><span>, </span><span><span class="hljs-number">0x01</span></span><span>, </span><span><span class="hljs-number">0x02</span></span><span>, </span><span><span class="hljs-number">0x03</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">bin2hex</span></span><span>(</span><span><span class="hljs-variable">$bin</span></span><span>); </span><span><span class="hljs-comment">// 输出 "010203"</span></span><span>

</span><span><span class="hljs-comment">// 拼接 chr 方式（等价）</span></span><span>
</span><span><span class="hljs-variable">$bin2</span></span><span> = </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">1</span></span><span>) . </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">2</span></span><span>) . </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">3</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">bin2hex</span></span><span>(</span><span><span class="hljs-variable">$bin2</span></span><span>); </span><span><span class="hljs-comment">// "010203"</span></span><span>
</span></span>

3) 生成 UTF-8 多字节字符（中文、表情等）

chr() 只返回单字节。UTF-8 多字节字符（代码点 > 0xFF）不能直接由 chr() 生成。常用替代方法包括：

方法 A — 使用 mb_convert_encoding() / html_entity_decode()（基于 HTML 实体）

对已知 Unicode 码点（如 U+1F600 表情）可通过 HTML 实体转换为 UTF-8：

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 使用 HTML 实体生成表情（例如 ?? U+1F600）</span></span><span>
</span><span><span class="hljs-variable">$emoji</span></span><span> = </span><span><span class="hljs-title function_ invoke__">html_entity_decode</span></span><span>(</span><span><span class="hljs-string">'&amp;#x1F600;'</span></span><span>, ENT_NOQUOTES, </span><span><span class="hljs-string">'UTF-8'</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$emoji</span></span><span> . PHP_EOL;
</span></span>

方法 B — 使用 IntlChar::chr()（如果安装了 intl 扩展）

如果服务器启用了 ext-intl，可以直接按 Unicode 代码点生成字符：

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 需要 ext-intl</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title class_">IntlChar</span></span><span>::</span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x4E2D</span></span><span>); </span><span><span class="hljs-comment">// 输出 "中"</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title class_">IntlChar</span></span><span>::</span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x1F600</span></span><span>); </span><span><span class="hljs-comment">// 输出 ??（表情）</span></span><span>
</span></span>

方法 C — 使用二进制字节（hex）——hex2bin() 生成特定 UTF-8 字节序列

已知字符的 UTF-8 十六进制字节序列时，可直接构造字节串：

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// "中" 的 UTF-8 编码是 E4 B8 AD</span></span><span>
</span><span><span class="hljs-variable">$zh</span></span><span> = </span><span><span class="hljs-title function_ invoke__">hex2bin</span></span><span>(</span><span><span class="hljs-string">'e4b8ad'</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$zh</span></span><span>; </span><span><span class="hljs-comment">// 输出 中</span></span><span>

</span><span><span class="hljs-comment">// 表情 ?? 的 UTF-8 编码是 F0 9F 98 80</span></span><span>
</span><span><span class="hljs-variable">$emoji</span></span><span> = </span><span><span class="hljs-title function_ invoke__">hex2bin</span></span><span>(</span><span><span class="hljs-string">'f09f9880'</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$emoji</span></span><span>; </span><span><span class="hljs-comment">// 输出 ??</span></span><span>
</span></span>

注意：这里 hex2bin() 直接写出 UTF-8 的字节值，适用于你已知字节序列的情况（例如来自规范或网络抓包）。

4) 处理 Unicode 码点到 UTF-8 的通用方法

如果你有一个整数码点，需要通用函数把它转成 UTF-8 字符（不依赖额外扩展），可以自己实现简单的转换（下面为示例实现）：

<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">codepoint_to_utf8</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">int</span></span></span><span> </span><span><span class="hljs-variable">$cp</span></span><span>): </span><span><span class="hljs-title">string</span></span><span> {
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$cp</span></span><span> &lt;= </span><span><span class="hljs-number">0x7F</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-variable">$cp</span></span><span>);
    } </span><span><span class="hljs-keyword">elseif</span></span><span> (</span><span><span class="hljs-variable">$cp</span></span><span> &lt;= </span><span><span class="hljs-number">0x7FF</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0xC0</span></span><span> | (</span><span><span class="hljs-variable">$cp</span></span><span> &gt;&gt; </span><span><span class="hljs-number">6</span></span><span>)) .
               </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x80</span></span><span> | (</span><span><span class="hljs-variable">$cp</span></span><span> &amp; </span><span><span class="hljs-number">0x3F</span></span><span>));
    } </span><span><span class="hljs-keyword">elseif</span></span><span> (</span><span><span class="hljs-variable">$cp</span></span><span> &lt;= </span><span><span class="hljs-number">0xFFFF</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0xE0</span></span><span> | (</span><span><span class="hljs-variable">$cp</span></span><span> &gt;&gt; </span><span><span class="hljs-number">12</span></span><span>)) .
               </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x80</span></span><span> | ((</span><span><span class="hljs-variable">$cp</span></span><span> &gt;&gt; </span><span><span class="hljs-number">6</span></span><span>) &amp; </span><span><span class="hljs-number">0x3F</span></span><span>)) .
               </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x80</span></span><span> | (</span><span><span class="hljs-variable">$cp</span></span><span> &amp; </span><span><span class="hljs-number">0x3F</span></span><span>));
    } </span><span><span class="hljs-keyword">elseif</span></span><span> (</span><span><span class="hljs-variable">$cp</span></span><span> &lt;= </span><span><span class="hljs-number">0x10FFFF</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0xF0</span></span><span> | (</span><span><span class="hljs-variable">$cp</span></span><span> &gt;&gt; </span><span><span class="hljs-number">18</span></span><span>)) .
               </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x80</span></span><span> | ((</span><span><span class="hljs-variable">$cp</span></span><span> &gt;&gt; </span><span><span class="hljs-number">12</span></span><span>) &amp; </span><span><span class="hljs-number">0x3F</span></span><span>)) .
               </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x80</span></span><span> | ((</span><span><span class="hljs-variable">$cp</span></span><span> &gt;&gt; </span><span><span class="hljs-number">6</span></span><span>) &amp; </span><span><span class="hljs-number">0x3F</span></span><span>)) .
               </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x80</span></span><span> | (</span><span><span class="hljs-variable">$cp</span></span><span> &amp; </span><span><span class="hljs-number">0x3F</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">'Invalid Unicode code point'</span></span><span>);
}

</span><span><span class="hljs-comment">// 使用</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">codepoint_to_utf8</span></span><span>(</span><span><span class="hljs-number">0x4E2D</span></span><span>);   </span><span><span class="hljs-comment">// 中</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">codepoint_to_utf8</span></span><span>(</span><span><span class="hljs-number">0x1F600</span></span><span>); </span><span><span class="hljs-comment">// ??</span></span><span>
</span></span>

这个函数内部仍然使用 chr() 构造每个 UTF-8 字节，是一种纯 PHP 的通用方案。

5) 常见陷阱与建议

chr() 的参数范围：只适用于单字节（0–255）。传入大于 255 的值会发生截断（取低 8 位），这通常不是你想要的行为。
编码环境：在处理多字节字符时确保字符串编码为 UTF-8 并且相关函数（例如 json_encode、strlen）时注意使用 mb_* 系列或指定正确编码。
显示与传输：某些环境（终端、HTTP 头、数据库列）对编码敏感。构造好 UTF-8 字符后，记得在输出或存储时声明正确编码（例如 HTML 页面加上 <meta charset="utf-8"> 或设置 Content-Type: text/html; charset=utf-8）。
首选工具：如果你只需要处理 Unicode 代码点，优先使用 IntlChar::chr()（若可用）或 mb_* / 转换函数，因为它们语义明确并少出错。

6) 快速参考表（小抄）

<span><span><span class="hljs-comment">// 单字节字符</span></span><span>
</span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">65</span></span><span>); </span><span><span class="hljs-comment">// "A"</span></span><span>
</span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">10</span></span><span>); </span><span><span class="hljs-comment">// LF 换行</span></span><span>

</span><span><span class="hljs-comment">// 多字节 / Unicode 替代</span></span><span>
</span><span><span class="hljs-title function_ invoke__">html_entity_decode</span></span><span>(</span><span><span class="hljs-string">'&amp;#x1F600;'</span></span><span>, ENT_NOQUOTES, </span><span><span class="hljs-string">'UTF-8'</span></span><span>); </span><span><span class="hljs-comment">// ??</span></span><span>
</span><span><span class="hljs-title class_">IntlChar</span></span><span>::</span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-number">0x4E2D</span></span><span>); </span><span><span class="hljs-comment">// "中"（需 ext-intl）</span></span><span>
</span><span><span class="hljs-title function_ invoke__">hex2bin</span></span><span>(</span><span><span class="hljs-string">'e4b8ad'</span></span><span>); </span><span><span class="hljs-comment">// "中"（直接用 UTF-8 十六进制字节）</span></span><span>

</span><span><span class="hljs-comment">// 自己把代码点转换为 UTF-8（见上面的 codepoint_to_utf8）</span></span><span>
</span></span>

总结

chr() 在生成单字节（0–255）字符和二进制数据时非常简单直接；但面对多字节的 Unicode 字符（中文、emoji）时，需要配合 IntlChar::chr()、HTML 实体转换、hex2bin() 或自定义的码点到 UTF-8 转换函数来实现可靠的结果。根据你的具体场景（网络协议、文件处理、网页输出）选择合适的方法并注意编码一致性，就能稳定生成各种“特殊字符”的字符串。