检查字符串是否是UTF8编码

转载地址： http://blog.qita.in/?post=418

1. function is_utf8($string){
2. return preg_match('%^(?:
3. [\x09\x0A\x0D\x20-\x7E] # ASCII
4. | [\xC2-\xDF][\x80-\xBF] # non-overlong 2-byte
5. | \xE0[\xA0-\xBF][\x80-\xBF] # excluding overlongs
6. | [\xE1-\xEC\xEE\xEF][\x80-\xBF]{2} # straight 3-byte
7. | \xED[\x80-\x9F][\x80-\xBF] # excluding surrogates
8. | \xF0[\x90-\xBF][\x80-\xBF]{2} # planes 1-3
9. | [\xF1-\xF3][\x80-\xBF]{3} # planes 4-15
10. | \xF4[\x80-\x8F][\x80-\xBF]{2} # plane 16
11. )*$%xs', $string);
12. }

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