如何设置csv文件列的大小？

我想在csv文件中设置每列的大小，我想根据字段设置列的大小，我不知道我可以在哪里做代码来设置大小？任何人都可以帮忙，将不胜感激，提前感谢。

这是我的代码

function export($result)
{   
    Configure::write('debug',0);
    $filename = "excel.".csv";
    $csv_file = fopen('php://output', 'w');
    header('Content-Type: text/csv; charset=utf-8');
    header('Content-Disposition: attachment; filename="'.$filename.'"');    

    // The column headings of  .csv file
    $header_row1 = array(   
                        "Last Name",
                        "First Name",
                        "Middle Name",
                        );

    $header_row =   array_merge($header_row1,$header_row2);
    fputcsv($csv_file,$header_row,',','"');

    // Array indexes correspond to the field names in your db table(s)
    if (!isset($result['Post']['User'])) {
        $row1 = array(
            $result['Post']['prefix_name'],
            $result['Post']['first_name'],
            $result['Post']['middle_name'],
            $result['Post']['last_name'],
        );
    }
    else {
            $row1 = array(
            $result['Post']['prefix_name'],
            $result['Post']['first_name'],
            $result['Post']['middle_name'],
            $result['Post']['last_name'],
        );
    }

    $row = array_merge($row1,$row2);

    unset($row2);
    fputcsv($csv_file,$row,',','"');
}

    fclose($csv_file);
    exit;
}