strcspn()

(PHP 4, PHP 5, PHP 7)

获取不匹配遮罩的起始子字符串的长度

说明

strcspn(string $str1, string $str2[,int $start[,int $length]]) : int

返回$str1中，所有字符都不存在于$str2范围的起始子字符串的长度。

参数

$str1

第一个字符串。

$str2

第二个字符串。

$start

查找的起始位置。

$length

查找的长度。

返回值

以整型数返回子串的长度。

范例

Example #1strcspn()example

<?php
$a = strcspn('abcd',  'apple');
$b = strcspn('abcd',  'banana');
$c = strcspn('hello', 'l');
$d = strcspn('hello', 'world');
var_dump($a);
var_dump($b);
var_dump($c);
var_dump($d);
?>

以上例程会输出：

int(0)
int(0)
int(2)
int(2)

注释

Note: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。

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.

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";
}
?>

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.

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').

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');
?>