php函数strcspn（）中的“start”参数是做什么的

i was trying to execute the following code

$string ='mynameisjenson';
echo strcspn( $string,'j',11);

the ouput am getting is 3 but really don't know how is gets 3.could any one please explain this

The start parameter tells strcspn() to start looking at that position in the string, instead of starting at the beginning of the string.

strcspn($string, 'j', 11)

is equivalent to

strcspn(substr($string, 11), 'j')

Position 11 in your string is the s character, so it's doing:

strcspn('son', 'j');

Since there's no j in that part of the string, it returns 3.