php判断编码格式的例子

// Returns true if $string is valid UTF-8 and false otherwise. 
function is_utf8($string) { 
     
    //  
    return preg_match('%^(?: 
          [x09x0Ax0Dx20-x7E]            # ASCII 
        | [xC2-xDF][x80-xBF]             # non-overlong 2-byte 
        |  xE0[xA0-xBF][x80-xBF]        # excluding overlongs 
        | [xE1-xECxEExEF][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); 
     
} // function is_utf8