php 检查字符串是否是UTF8编码

function is_utf8($string){
    return preg_match('%^(?:
         [\\x09\\x0A\\x0D\\x20-\\x7E]            # ASCII
       | [\\xC2-\\xDF][\\x80-\\xBF]             # non-overlong 2-byte
       |  \\xE0[\\xA0-\\xBF][\\x80-\\xBF]        # excluding overlongs
       | [\\xE1-\\xEC\\xEE\\xEF][\\x80-\\xBF]{2}  # straight 3-byte
       |  \\xED[\\x80-\\x9F][\\x80-\\xBF]        # excluding surrogates
       |  \\xF0[\\x90-\\xBF][\\x80-\\xBF]{2}     # planes 1-3
       | [\\xF1-\\xF3][\\x80-\\xBF]{3}          # planes 4-15
       |  \\xF4[\\x80-\\x8F][\\x80-\\xBF]{2}     # plane 16
   )*$%xs', $string);
}
//该片段来自于http://outofmemory.cn