如何在PHP中使用strcspn函数？快速入门教程！

gitbox 2025-08-16

在PHP中，strcspn 函数是一个非常实用的字符串处理函数，它用来返回从字符串开头开始，直到遇到任何一个指定字符时，所经过的字符数量。这个函数特别适用于处理字符串中不包含某些字符的部分，或者在寻找某些特定字符时，需要获取它们的相对位置。

strcspn 函数的语法

<span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$haystack</span></span><span>, </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$charlist</span></span><span>, </span><span><span class="hljs-keyword">int</span></span><span> </span><span><span class="hljs-variable">$start</span></span><span> = </span><span><span class="hljs-number">0</span></span><span>, </span><span><span class="hljs-keyword">int</span></span><span> </span><span><span class="hljs-variable">$length</span></span><span> = </span><span><span class="hljs-literal">NULL</span></span><span>): </span><span><span class="hljs-keyword">int</span></span><span>
</span></span>

参数说明：

$haystack：目标字符串，即你要检查的字符串。
$charlist：指定的字符列表，strcspn 会扫描 $haystack 字符串，直到找到列表中的任意字符。
$start（可选）：指定开始搜索的位置，默认为 0。
$length（可选）：限定搜索的字符长度，默认为 NULL，表示搜索整个字符串。

函数返回值

strcspn 函数返回一个整数值，表示从字符串开始处到遇到任何一个 $charlist 中字符的位置（或遇到字符列表中的字符时，返回扫描到的位置）。如果没有遇到任何指定字符，则返回整个字符串的长度。

使用示例

让我们通过几个简单的示例来展示 strcspn 函数的用法。

示例 1：查找指定字符在字符串中的位置

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"Hello, World!"</span></span><span>;
</span><span><span class="hljs-variable">$characters</span></span><span> = </span><span><span class="hljs-string">" ,!"</span></span><span>;
</span><span><span class="hljs-variable">$position</span></span><span> = </span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, </span><span><span class="hljs-variable">$characters</span></span><span>);

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"The first occurrence of a character from the list is at position: <span class="hljs-subst">$position</span></span></span><span>";
</span><span><span class="hljs-comment">// 输出：The first occurrence of a character from the list is at position: 5</span></span><span>
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

在这个例子中，strcspn 从字符串 "Hello, World!" 开始，直到遇到字符 ' '（空格）为止。它返回的结果是 5，表示第六个字符是空格（数组索引从0开始）。

示例 2：指定开始搜索的位置

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"Hello, World!"</span></span><span>;
</span><span><span class="hljs-variable">$characters</span></span><span> = </span><span><span class="hljs-string">" ,!"</span></span><span>;
</span><span><span class="hljs-variable">$position</span></span><span> = </span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, </span><span><span class="hljs-variable">$characters</span></span><span>, </span><span><span class="hljs-number">6</span></span><span>);

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"The first occurrence of a character from the list after position 6 is at: <span class="hljs-subst">$position</span></span></span><span>";
</span><span><span class="hljs-comment">// 输出：The first occurrence of a character from the list after position 6 is at: 8</span></span><span>
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

在此示例中，我们指定从第6个字符开始查找。即使空格字符在第5个位置，函数也会从位置6开始寻找，直到遇到下一个空格字符 ' '，结果返回的是8。

示例 3：不指定字符列表

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"123456789"</span></span><span>;
</span><span><span class="hljs-variable">$position</span></span><span> = </span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, </span><span><span class="hljs-string">"678"</span></span><span>);

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"The first occurrence of a character from the list is at position: <span class="hljs-subst">$position</span></span></span><span>";
</span><span><span class="hljs-comment">// 输出：The first occurrence of a character from the list is at position: 6</span></span><span>
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>

在这个例子中，strcspn 将查找字符串中是否有 '6', '7' 或 '8'。函数返回的位置是第6个字符（即字符 '6'），表示 678 这个字符列表首次出现的位置。

实际应用场景

清除不必要的字符：
strcspn 可以用来清除字符串中的无关字符。例如，提取一个包含数字的字符串，并删除非数字字符。

<span><span><span class="hljs-variable">$input</span></span><span> = </span><span><span class="hljs-string">"abc123xyz"</span></span><span>;
</span><span><span class="hljs-variable">$digits</span></span><span> = </span><span><span class="hljs-title function_ invoke__">substr</span></span><span>(</span><span><span class="hljs-variable">$input</span></span><span>, </span><span><span class="hljs-number">0</span></span><span>, </span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-variable">$input</span></span><span>, </span><span><span class="hljs-string">"abcdefghijklmnopqrstuvwxyz"</span></span><span>));
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Extracted digits: <span class="hljs-subst">$digits</span></span></span><span>"; </span><span><span class="hljs-comment">// 输出：Extracted digits: 123</span></span><span>
</span></span>

密码验证：
如果你希望检测一个密码是否包含非法字符（例如控制字符或空格），strcspn 是一个非常合适的工具。

<span><span><span class="hljs-variable">$password</span></span><span> = </span><span><span class="hljs-string">"secure@123"</span></span><span>;
</span><span><span class="hljs-variable">$illegalChars</span></span><span> = </span><span><span class="hljs-string">" \t\r\n"</span></span><span>;
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-variable">$password</span></span><span>, </span><span><span class="hljs-variable">$illegalChars</span></span><span>) == </span><span><span class="hljs-title function_ invoke__">strlen</span></span><span>(</span><span><span class="hljs-variable">$password</span></span><span>)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Password is valid!"</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">"Password contains illegal characters!"</span></span><span>;
}
</span></span>

文本清理：
假设你有一段文本，其中可能包含一些标点符号，使用 strcspn 可以轻松提取第一个无标点的部分。

总结

strcspn 函数是一个高效且灵活的字符串处理工具，它帮助开发者定位某些字符在字符串中的位置，或从字符串中截取有效部分。通过掌握该函数的使用，能够有效地处理和分析字符串数据，提升代码的清晰度和可维护性。

strcspn