Problems with regular matching pattern modifier lowercase u php

Regular match pattern modifier lowercase u problem php
Recently seen a piece of code:

 
  $str = ' Hello, world dd ';
Preg_match_all ('/./us ', $str, $match);
echo Count ($match [0]). "
";  
?>

On the internet to check a lot of information, but for the PHP regular expression pattern modifier u really some do not understand, solve ah ...

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------Solution--------------------
The u:unicode abbreviation, which indicates that the string to be matched is a string conforming to the Unicode encoding rules, such as a utf-8 encoded string
Under the U modifier, a kanji is treated as a character. \w has the original [_0-9a-za-z] extended to Chinese characters
------Solution--------------------

$s = ' Chinese abc ';
Preg_match_all ('/\w/', $s, $r); No U-Decoration
Print_r ($R);

Have
Array
(
[0] = = Array
(
[0] = a
[1] = b
[2] = C
)

)

$s = ' Chinese abc ';
Preg_match_all ('/\w/u ', $s, $r); With U-modifier
Print_r ($R);

Have
Array
(
[0] = = Array
(
[0] = Han
[1] = Word
[2] = a
[3] = b
[4] = C
)

)

------Solution--------------------
References:

$s = ' Chinese abc ';
Preg_match_all ('/\w/', $s, $r); No U-Decoration
Print_r ($R);

Have
Array
(
[0] = = Array
(
[0] = a
[1] = b
[2] = C
)

)

$s = ' Chinese abc ';
Preg_match_all ('/\w/u ', $s, $r); With U-modifier
Print_r ($R);

Have
Array
(
[0] = = Array
(
[0] = Han
[1] = Word
[2] = a
[3] = b
[4] = C
)

)

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This person writes. NET easy to understand, ask moderator greatly similar to a ...

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