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English
In PHP, the strcspn function is used to calculate the position of the first character in a string that does not belong to a specified set of characters. Its full name is "string complement span," meaning it starts scanning from the beginning of the string, finds the first character not included in the given character set, and returns its index position. This function is often used in string processing, especially when you need to find the first occurrence of a particular character in a string.
<span><span><span class="hljs-keyword">int</span></span><span> </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">$start</span></span> = </span><span><span class="hljs-number">0</span></span><span> [, </span><span><span class="hljs-keyword">int</span></span><span> </span><span><span class="hljs-variable">$length</span></span> = </span><span><span class="hljs-literal">NULL</span></span><span> ]])
</span></span>$haystack: The target string to be searched.
$charlist: The set of characters to check against, represented as a string containing multiple characters.
$start: Optional. Specifies the starting position for the search. Default is 0.
$length: Optional. Specifies the maximum length to check. Default is NULL, which means searching continues from $start until the end of the string.
The strcspn function starts scanning the given string $haystack and looks for the first character that does not belong to the $charlist. It then returns the position of that character. The returned value is the zero-based index of the character in the string.
For example, if you have the string abcdef and the character set abc, strcspn will return the position of the first character not in the set abc, which is d at index 3.
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-comment">// Example string</span></span><span>
</span><span><span class="hljs-variable">$str</span></span><span> = </span><span><span class="hljs-string">"abcdef"</span></span><span>;
</span><span><span class="hljs-comment">// Define character set</span></span><span>
</span><span><span class="hljs-variable">$charlist</span></span><span> = </span><span><span class="hljs-string">"abc"</span></span><span>;
<p></span>// Use strcspn to find the first character not in the set<br>
$position = strcspn($str, $charlist);</p>
<p>// Output result<br>
echo "The position of the first character not in the set is: " . $position;<br>
?><br>
</span>Output:
<span><span><span class="hljs-section">The position of the first character not in the set is: 3</span></span><span>
</span></span>In this example, the string "abcdef" begins with characters a, b, and c. Once it encounters d, which is not in the set abc, the returned position is 3.
Check if characters belong to a specific set: During data processing or validation, strcspn can help verify whether input contains invalid or unwanted characters. For example, checking if a username only contains letters or digits.
Extract substrings: If you need to extract all characters before a certain character in a string, you can use strcspn together with substr. For example, to extract everything before the first digit:
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-variable">$input</span></span><span> = </span><span><span class="hljs-string">"abc123xyz"</span></span><span>;
</span><span><span class="hljs-variable">$position</span></span><span> = </span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-variable">$input</span></span><span>, </span><span><span class="hljs-string">'0123456789'</span></span><span>);
</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">substr</span></span><span>(</span><span><span class="hljs-variable">$input</span></span><span>, </span><span><span class="hljs-number">0</span></span>, </span><span><span class="hljs-variable">$position</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$result</span></span><span>; </span><span><span class="hljs-comment">// Outputs "abc"</span></span><span>
</span><span><span class="hljs-meta">?></span></span><span>
</span></span>This code returns "abc", because it extracts all characters before the digit 1.
Handle special character sets: If you need to find special characters or whitespace in a string, strcspn is also useful. For instance, locating the first space or punctuation mark:
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-variable">$input</span></span><span> = </span><span><span class="hljs-string">"hello, world!"</span></span><span>;
</span><span><span class="hljs-variable">$position</span></span><span> = </span><span><span class="hljs-title function_ invoke__">strcspn</span></span><span>(</span><span><span class="hljs-variable">$input</span></span><span>, </span><span><span class="hljs-string">' ,.!'</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"The position of the first character not being space, comma, period, or exclamation mark is: "</span></span><span> . </span><span><span class="hljs-variable">$position</span></span><span>;
</span><span><span class="hljs-meta">?></span></span><span>
</span></span>This snippet helps filter out common punctuation and return the actual content of the string.
strcspn is a powerful PHP string-handling function that allows developers to precisely locate characters in a string that are not part of a specified set. In real-world development, especially in string validation and parsing tasks, strcspn proves to be a very practical tool that can improve both efficiency and readability of the code. Mastering this function makes string operations more flexible and efficient.
