PHP8.0 thinkphp 6 msubstr()函数 报错Deprecated: Required parameter $length follows optional parameter $start in

function msubstr( $str , $start =0, $length , $charset = "utf-8" , $suffix =true)

{

   if (function_exists( "mb_substr" )){

     if ( $suffix )

        return mb_substr( $str , $start , $length , $charset ). "..." ;

     else

        return mb_substr( $str , $start , $length , $charset );

   }

   elseif (function_exists( 'iconv_substr' )) {

     if ( $suffix )

        return iconv_substr( $str , $start , $length , $charset ). "..." ;

     else

        return iconv_substr( $str , $start , $length , $charset );

   }

   $re [ 'utf-8' ]  = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|[\xe0-\xef][\x80-\xbf]{2}|[\xf0-\xff][\x80-\xbf]{3}/" ;

   $re [ 'gb2312' ] = "/[\x01-\x7f]|[\xb0-\xf7][\xa0-\xfe]/" ;

   $re [ 'gbk' ]  = "/[\x01-\x7f]|[\x81-\xfe][\x40-\xfe]/" ;

   $re [ 'big5' ]  = "/[\x01-\x7f]|[\x81-\xfe]([\x40-\x7e]|\xa1-\xfe])/" ;

   preg_match_all( $re [ $charset ], $str , $match );

   $slice = join( "" , array_slice ( $match [0], $start , $length ));

   if ( $suffix ) return $slice . "…" ;

   return $slice ;

}

======================解决办法=======================

修改$length默认长度；
function msubstr( $str , $start =0, $length=999 , $charset = "utf-8" , $suffix =true)