strspn()

(PHP 4, PHP 5, PHP 7)

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。

说明

返回$subject中全部字符仅存在于$mask中的第一组连续字符(子字符串)的长度。

如果省略了$start和$length参数，则检查整个$subject字符串；如果指定了这两个参数，则效果等同于调用strspn(substr($subject,$start,$length),$mask)（更多信息，参见substr）。

代码行：

参数

待检查的字符串。

检查字符列表。

$subject的开始检查位置。

如果$start被设置并且是非负的，strspn()将从$subject的第$start个位置开始检查。例如，在字符串'abcdef'中，第0个位置的字符是'a'，第二个位置的字符是'c'，等等。

如果$start被设置并且为负数，strspn()将从$subject的尾部倒数第$start个位置开始检查$subject。

$subject中检查的长度。

如果$length被设置并且为非负数，那么将从起始位置开始，检查$subject的$length个长度的字符。

如果$length被设置并且为负数，那么将从起始位置开始，直到从$subject尾部开始第$length个位置，对$subject进行检查。

返回值

返回$str1中第一段全部字符都存在于$str2范围的字符串的长度。

更新日志

范例

Example #1strspn()范例

以上例程会输出：

int(0)
int(2)
int(1)

注释

Note:此函数可安全用于二进制对象。

参见

• strcspn()获取不匹配遮罩的起始子字符串的长度

you can use this function with strlen to check illegal characters, string lenght must be the same than strspn (characters from my string contained in another)

It took me some time to understand the way this function works…
I’ve compiled my own explanation with my own words that is more understandable for me personally than the official one or those that can be found in different tutorials on the web.
Perhaps, it will save someone several minutes…

The way it works:
 -  searches for a segment of $haystack that consists entirely from supplied through the second argument chars 
 -  $haystack must start from one of the chars supplied through $char_list, otherwise the function will find nothing
 -  as soon as the function encounters a char that was not mentioned in $chars it understands that the segment is over and stops (it doesn’t search for the second, third and so on segments)
 -  finally, it measures the segment’s length and return it (i.e. length)
In other words it finds a span (only the first one) in the string that consists entirely form chars supplied in $chars_list and returns its length

This function is significantly faster for checking illegal characters than the equivalent preg_match() method.

Quick way to check if a string consists entirely of characters within the mask is to compare strspn with strlen eg:

very dificult to get from the definition directly, while i search for that,i came to know that
strspn() will tell you the length of a string consisting entirely of the set of characters in accept set. That is, it starts walking down str until it finds a character that is not in the set (that is, a character that is not to be accepted), and returns the length of the string so far. 
and 
strcspn() works much the same way, except that it walks down str until it finds a character in the reject set (that is, a character that is to be rejected.) It then returns the length of the string so far.

hope this example will help in understanding the concept of strspn() and strcspn().

The second parameter is a set of allowed characters.
strspn will return an zero-based index of a first non-allowed character.

strspon and preg_match seem to be equally fast for validating numbers:

This function doesn't work with non ASCII characters
Exemple:

See, we expected 1 but 0 was the correct result

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