How to output mysqli_fetch_field_direct?

I’m trying to convert this code from mysql to mysqli. But when I print it and open in excel file I got an error.

Catchable fatal error: Object of class stdClass could not be converted to string in C:xampplitehtdocsapptext2.php on line 139

Can someone Teach me how to convert this code in mysqli correctly?

<?PHP

//EDIT YOUR MySQL Connection Info:
$DB_Server = "localhost";        //your MySQL Server
$DB_Username = "root";                 //your MySQL User Name
$DB_Password = "";                //your MySQL Password
$DB_DBName = "app";                //your MySQL Database Name
$DB_TBLName = "purchase_order";                //your MySQL Table Name
$mysqli = new mysqli("localhost", "root", "", "app"); 
//$DB_TBLName,  $DB_DBName, may also be commented out & passed to the browser
//as parameters in a query string, so that this code may be easily reused for
//any MySQL table or any MySQL database on your server
if (isset($_POST['supp'])) {
$var = $_POST['supp'];
//DEFINE SQL QUERY:
//edit this to suit your needs
$result = $mysqli->query("Select id, counter, supplier, quantity, unit_cost, SUM(quantity*unit_cost) total_amount from $DB_TBLName where supplier='$var' GROUP BY id");
}
//Optional: print out title to top of Excel or Word file with Timestamp
//for when file was generated:
//set $Use_Titel = 1 to generate title, 0 not to use title
$Use_Title = 1;
//define date for title: EDIT this to create the time-format you need
$now_date = DATE('m-d-Y H:i');
//define title for .doc or .xls file: EDIT this if you want
$title = "Dump For Table $DB_TBLName from Database $DB_DBName on $now_date";
/*

Leave the connection info below as it is:
just edit the above.

(Editing of code past this point recommended only for advanced users.)
*/
//create MySQL connection

//execute query



//if this parameter is included ($w=1), file returned will be in word format ('.doc')
//if parameter is not included, file returned will be in excel format ('.xls')
IF (ISSET($w) && ($w==1))
{
     $file_type = "msword";
     $file_ending = "doc";
}ELSE{
     $file_type = "vnd.ms-excel";
     $file_ending = "xls";
}
//header info for browser: determines file type ('.doc' or '.xls')
HEADER("Content-Type: application/$file_type");
HEADER("Content-Disposition: attachment; filename=MDT_DB_$now_date.$file_ending");
HEADER("Pragma: no-cache");
HEADER("Expires: 0");

/*    Start of Formatting for Word or Excel    */

IF (ISSET($w) && ($w==1)) //check for $w again
{
     /*    FORMATTING FOR WORD DOCUMENTS ('.doc')   */
     //create title with timestamp:
     IF ($Use_Title == 1)
     {
         //ECHO("$titlenn");
     }
     //define separator (defines columns in excel & tabs in word)
     $sep = "n"; //new line character
while($row = $result->mysqli_fetch_row())
     {
         //set_time_limit(60); // HaRa
         $schema_insert = "";
         FOR($j=0; $j<mysqli_num_fields($result);$j++)
         {
         //define field names
         $field_name = mysqli_fetch_field_direct($result,$j);
         //will show name of fields
         $schema_insert .= "$field_name:t";
             IF(!ISSET($row[$j])) {
                 $schema_insert .= "NULL".$sep;
                 }
             ELSEIF ($row[$j] != "") {
                 $schema_insert .= "$row[$j]".$sep;
                 }
             ELSE {
                 $schema_insert .= "".$sep;
                 }
         }
         $schema_insert = STR_REPLACE($sep."$", "", $schema_insert);
         $schema_insert .= "t";
         PRINT(TRIM($schema_insert));
         //end of each mysql row
         //creates line to separate data from each MySQL table row
         PRINT "n----------------------------------------------------n";
     }
}ELSE{
     /*    FORMATTING FOR EXCEL DOCUMENTS ('.xls')   */
     //create title with timestamp:
     IF ($Use_Title == 1)
     {
         //ECHO("$title");
     }
     //define separator (defines columns in excel & tabs in word)
     $sep = "t"; //tabbed character

     //start of printing column names as names of MySQL fields
     FOR ($i = 0; $i < mysqli_num_fields($result); $i++)
     {
         ECHO mysqli_fetch_field_direct($result,$i) . "t";
     }
     PRINT("n");
     //end of printing column names

     //start while loop to get data
     while($row = $result->mysqli_fetch_row())
     {
         //set_time_limit(60); // HaRa
         $schema_insert = "";
         FOR($j=0; $j<mysqli_num_fields($result);$j++)
         {
             IF(!ISSET($row[$j]))
                 $schema_insert .= "NULL".$sep;
             ELSEIF ($row[$j] != "")
                 $schema_insert .= "$row[$j]".$sep;
             ELSE
                 $schema_insert .= "".$sep;
         }
         $schema_insert = STR_REPLACE($sep."$", "", $schema_insert);
         //following fix suggested by Josue (thanks, Josue!)
         //this corrects output in excel when table fields contain n or r
         //these two characters are now replaced with a space
         $schema_insert = PREG_REPLACE("/rn|nr|n|r/", " ", $schema_insert);
         $schema_insert .= "t";
         PRINT(TRIM($schema_insert));
         PRINT "n";
     }
}
?>

And this the error line

 137    FOR ($i = 0; $i < mysqli_num_fields($result); $i++)
 138    {
 139        ECHO mysqli_fetch_field_direct($result,$i) . "t";
 140    }

Answer

You can not echo out the output from mysqli_fetch_field_direct() because it:

Returns an object which contains field definition information from the specified result set.

instead try something like this (from PHP docs) to get a sense of what the returned object contains:

$finfo = mysqli_fetch_field_direct($result,$i);

printf("Name:     %sn", $finfo->name);
printf("Table:    %sn", $finfo->table);
printf("max. Len: %dn", $finfo->max_length);
printf("Flags:    %dn", $finfo->flags);
printf("Type:     %dn", $finfo->type);