如何在PHP中使用strcspn函數？快速入門教程！

gitbox 2025-08-16

在PHP中， strcspn函數是一個非常實用的字符串處理函數，它用來返回從字符串開頭開始，直到遇到任何一個指定字符時，所經過的字符數量。這個函數特別適用於處理字符串中不包含某些字符的部分，或者在尋找某些特定字符時，需要獲取它們的相對位置。

strcspn 函數的語法

<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>

參數說明：

$haystack ：目標字符串，即你要檢查的字符串。
$charlist ：指定的字符列表， strcspn會掃描$haystack字符串，直到找到列表中的任意字符。
$start （可選）：指定開始搜索的位置，默認為0 。
$length （可選）：限定搜索的字符長度，默認為NULL ，表示搜索整個字符串。

函數返回值

strcspn函數返回一個整數值，表示從字符串開始處到遇到任何一個$charlist中字符的位置（或遇到字符列表中的字符時，返回掃描到的位置）。如果沒有遇到任何指定字符，則返回整個字符串的長度。

使用示例

讓我們通過幾個簡單的示例來展示strcspn函數的用法。

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">// 輸出：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>

在這個例子中， strcspn從字符串"Hello, World!"開始，直到遇到字符' ' （空格）為止。它返回的結果是5 ，表示第六個字符是空格（數組索引從0開始）。

示例2：指定開始搜索的位置

<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">// 輸出：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，我們指定從第6個字符開始查找。即使空格字符在第5個位置，函數也會從位置6開始尋找，直到遇到下一個空格字符' ' ，結果返回的是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">// 輸出：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>

在這個例子中， strcspn將查找字符串中是否有'6' , '7'或'8' 。函數返回的位置是第6個字符（即字符'6' ），表示678這個字符列表首次出現的位置。

實際應用場景

清除不必要的字符：
strcspn可以用來清除字符串中的無關字符。例如，提取一個包含數字的字符串，並刪除非數字字符。

 <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">// 輸出：Extracted digits: 123</span></span><span>
</span></span>

密碼驗證：
如果你希望檢測一個密碼是否包含非法字符（例如控製字符或空格）， strcspn是一個非常合適的工具。

 <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：
假設你有一段文本，其中可能包含一些標點符號，使用strcspn可以輕鬆提取第一個無標點的部分。

總結

strcspn函數是一個高效且靈活的字符串處理工具，它幫助開發者定位某些字符在字符串中的位置，或從字符串中截取有效部分。通過掌握該函數的使用，能夠有效地處理和分析字符串數據，提升代碼的清晰度和可維護性。

strcspn