php-如何在CodeIgniter中将查询结果对象转换为字符串

我的控制器中有以下代码：

    $sql = "SELECT MAX(roll) FROM student WHERE department = '".$this->db->escape_str($sdata['department'])."'";
    $query = $this->db->query($sql);

没错.我正在获得期望值.

但是,当我尝试在其他地方将此值用作字符串时,如下所示：

   $rolltext = substr($query->result(), 9);
   print_r($rolltext);
   die();

然后在localhost中运行该应用程序,出现以下错误：

    A PHP Error was encountered

    Severity: Warning

    Message: substr() expects parameter 1 to be string, array given

我知道变量$rolltext以数组而不是字符串的形式获取查询结果,这在substr()函数的语法方面是不正确的.这就是为什么我会收到此错误.我的问题是：如何将查询结果转换为字符串并在后续行中执行substr()操作？我没有在CodeIgniter用户指南中找到针对这种情况的特定解决方案/指南,这就是为什么我在这里询问.

解决方法:

请尝试以下操作：

 $sql = "SELECT MAX(roll) as maxroll FROM student WHERE department = '".$this->db->escape_str($sdata['department'])."'";
 $query = $this->db->query($sql);
 //$result = $query->result();  //  returns the query result as an array of objects
 $result = $query->row(); // returns a single result row
 $rolltext = substr( $result->maxroll, 9);

Note:

The Syntax for accessing values from query resultset is :

$result->fieldname;

where $result is the resultset and fieldname is the name of the
field you want the output of in your query.