KiloBug's Blog

function mb_substr($str, $start = 0, $length = 0, $encode = 'utf-8') {
    /* 该编码每个非英文字符的字节长度 */
    $encode_len = $encode == 'utf-8' ? 3 : 2;
    /* 计算开始字节 */
    for($byteStart = $i = 0; $i < $start; ++$i) {
        $byteStart += ord($str{$byteStart}) < 128 ? 1 : $encode_len;
        /* 当起始坐标超出字符串，则返回空值 */
        if( $str{$byteStart} == '' ) return '';
    }
    /* 计算字节长度 */
    for($i = 0, $byteLen = $byteStart; $i < $length; ++$i)
        $byteLen += ord($str{$byteLen}) < 128 ? 1 : $encode_len;
 
    return substr( $str, $byteStart, $byteLen-$byteStart );
}