about issues with releasing a database result set

Questions about freeing the database result set.
Class db{
private $host;//Service Area Address
private $user;//Login account
private $pass;//Login password
private $name;//Database name
private $font;//Database Character set
private $conn;//Database connection source
private $result;//Result set
private $rowRst;//Query a single record
Private $rowArray =array ();//Query multiple records
private $rowAff;//Increase in the number of deleted record strips

Public function __construct ($host, $user, $pass, $name, $font) {
$this->host= $host;
$this->user= $user;
$this->pass= $pass;
$this->name= $name;
$this->font= $font;
$this->init_conn ();
}

Connecting to a database
Private Function Init_conn () {
if (! $this->conn=mysql_connect ($this->host, $this->user, $this->pass)) {
Exit (' Database connection error ');
}
if (!mysql_select_db ($this->name, $this->conn)) {
Exit (' Database selection error ');
}
if (!mysql_query (' SET NAMES '. $this->font)) {
Exit (' character set error ');
}
}

Execute SQL statement
Public Function _query ($sql) {
if (! $this->result=mysql_query ($sql, $this->conn)) {
Exit (' SQL execution failed ');
}
return $this->result;
}

Querying heads-up data
Public Function _fetch_array ($sql) {
$this->_query ($sql);
$this->rowrst=mysql_fetch_array ($this->RESULT,MYSQL_ASSOC);
return $this->rowrst;
}

Querying more than one piece of data
Public Function _fetch_array_list ($sql) {
$this->_query ($sql);
while (!! $rows =mysql_fetch_array ($this->result,mysql_assoc)) {
$this->rowarray[]= $rows;
}
return $this->rowarray;
}

Number of affected records of the increase and deletion
Public Function _affected_rows () {
$this->rowaff=mysql_affected_rows ();
return $this->rowaff;
}

Gets the ID number of the insert operation in the previous step
Public Function _insert_id () {
return mysql_insert_id ();
}

Releasing the result set
Public Function _free_result () {
$this->rowaff= ';
$this->rowarray= ';
$this->rowrst= ';
Mysql_free_result ($this->result);
}

Close the database
Public Function _close_conn () {
$this->_free_result ();
Mysql_close ($this->conn);
}
}
When I use _close_conn this method is, the web surface displays Mysql_free_result (): supplied argument is not a valid MySQL result resource
How to solve this problem


------Solution--------------------
In Mysql_free_result ($this->result); Before you look at what $this->result become. is not the resource you originally opened
------Solution--------------------
if (Is_resource ($this->result))
{
Mysql_free_result ($this->result);
$this->result = NULL;
}
------Solution--------------------
Your $this->result is so assigned.
$this->result=mysql_query ($sql, $this->conn)

Mysql_query only the resource is returned when the SELECT statement is executed, the other is the logical value

So Mysql_free_result ($this->result);
To write
if (Is_resource ($this->result)) mysql_free_result ($this->result);

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