strcspn

(PHP 4, PHP 5, PHP 7, PHP 8)

strcspn — 获取不匹配遮罩的起始子字符串的长度

说明

function strcspn(
    string $string,
    string $characters,
    int $offset = 0,
    ?int $length = null
): int

返回 string 中，所有字符都不存在于 characters 范围的起始子字符串的长度。

如果省略 offset 和 length，则将检查所有的 string。如果包含前面两个参数，那么跟调用 strcspn(substr($string, $offset, $length), $characters) 效果相同（参阅 substr 获取更新信息）。

参数

string

要检查的字符串。

characters

包含每个不允许的字符的字符串。

offset

string 开始搜索的位置。

如果给出的 offset 是非负数，然后 strcspn() 将会从 string 的 offset 位置开始检查字符串。例如。在字符串“abcdef”中，位置为 0 的字符是“a”，位置为 2 的字符是“c”，等等。

如果给出的 offset 是负数，则 strcspn() 将会从距离 string 末尾的第 offset 个位置开始检查字符串。

length

要检查的部分 string 的长度。

如果给出的 length 是非负数，然后将检查 string 中起始位置后的 length 字符。

If length is given and is negative, then string will be examined from the starting position up to length characters from the end of string.

返回值

Returns the length of the initial segment of string which consists entirely of characters not in characters.

注意:
当设置了 offset 参数时，返回的长度是从该位置开始计算，而不是从 string 的开头计算。

更新日志

版本	说明
8.4.0	在 PHP 8.4.0 之前，当 `characters` 为空字符串时，搜索会错误地停止在 `string` 的第一个 null 字节处。
8.0.0	`length` 现在允许为 null。

示例

示例 #1 strcspn() 示例

<?php
$a = strcspn('banana', 'a');
$b = strcspn('banana', 'abcd');
$c = strcspn('banana', 'z');
$d = strcspn('abcdhelloabcd', 'a', -9);
$e = strcspn('abcdhelloabcd', 'a', -9, -5);

var_dump($a);
var_dump($b);
var_dump($c);
var_dump($d);
var_dump($e);
?>

以上示例会输出：

int(1)
int(0)
int(6)
int(5)
int(4)

注释

注意: 此函数可安全用于二进制对象。

参见

strspn() - 计算字符串中全部字符都存在于指定字符集合中的第一段子串的长度

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＋添加备注

用户贡献的备注 5 notes

down

AT-HE (at_he AT hotmai1 DOT com) ¶

20 years ago

this function can be used like strspn(), except while that can be used to compare a string with an allowed pattern, this one can be use to compare a string with a FORBIDDEN pattern

so, to know if any forbidden character has a position inside our string, we can use (not tested with backslashes)...

<?php
// LARGE VERSION
$forbidden="\"\\?*:/@|<>";
if (strlen($filename) != strcspn($filename,$forbidden)) {
    echo "you cant create a file with that name!";
}

// SHORT VERSION
if (strlen($filename) - strcspn($filename,"\"\\?*:/@|<>")) {
    echo "i told you, you cant create that file";
}
?>

down

maskedcoder at hotmail dot com ¶

20 years ago

useful for finding beginning of quotes and/or tags in a variable containing html.  
    $pos = strcspn($data, '<"\''); 
will find the first occurance of either the beginning of a tag, or a double- or single-quoted string.

down

legacyprog at routinz dot net ¶

15 years ago

When you use the third parameter remember that the function will return the number of characters it bypassed, which will *not* be the position in your source string.  It's a simple fix to just add your third parameter value to the function result to get the position in the first string where the scan stopped, but I didn't think of it at first.

down

Anonymous ¶

16 years ago

strcspn() can also be thought of as analogous to the following regular expression:
<?php
// where ... represents the mask of characters
preg_match('/[^ ...]/', substr($subject, $start, $length) );
?>
By this analogy, strcspn() can be used in place of some regular expressions to match a pattern without the overhead of a regex engine -- for example, ways to verify if an input string represents a binary value:
<?php
preg_match('/^[01]+$/i', $subject);
// or...
!preg_match('/[^01]/i', $subject);

// ...or using strcspn()
!strcspn($subject, '01');
?>

down

nospam at nospam dot com ¶

9 years ago

It might not be clear from the example, that

strcspn('abcdhelloabcd', 'abcd', -9, -5) == 4

because it's only evaluating 'hell' which doesn't contain any mask, so returns strlen('hell').