PHP's destructor study notes

__destruct ()

This method is automatically called internally by the system when the object is destroyed.

Divided into three categories:

　1. This method is automatically called when the PHP code declaration period finishes;

2. When the object is unset (), the system automatically calls the method

3. When the object is re-assigned, the system automatically calls the method

1 classtest{2 3              Public function__destruct () {4 5                 Echo"The code executed after the object is destroyed";6             }7         }8 9         $test=NewTest ();Ten  One         unset($test); A  -         $test= ' AAAA '; -  the what is the function of the destructor: - is a snippet of code that executes when a resource object is created to close a connection after it has finished running - The connection needs to be closed after the MySQL data connection is completed -         fopen() Close when the open file handle finishes executing + destroy session after session end, destroy () -  +  A  at the function of the destructor: - ensure data persistence updates.  - Each object corresponds to each record of a table in the database.  -  - CREATE TABLE Student ( -Sid int Unsigned PrimaryKeyAuto_increment, inName varchar (+) notNULL, -Gender nuem (' Male ', ' female ') notNULL to             )     +  -  the             classStudent { *                  Public $sid; $                  Public $name;Panax Notoginseng                  Public $gender; -  the                  Public function__construct ($sid){//when creating an object +                     $sql= "Select Sid,name,gender from student where Sid =$sid"; A                 } the  +                  Public functionSave () {//after the data is updated, it needs to be saved after each update.  -                     $sql= "Update student set Name=$this->name, gender=$this->gender WHERE sid =$sid"; $                 } $  -                  Public function__destruct () {//actions that need to be synchronized to the database after each update of student information -                     $this-Save ();  the                 } -             }Wuyi  the             $s=NewStudent (); -             $s->name = ' Xujin '; Wu             $s->save ();//This function is called every time because updating the data requires a synchronous update of the database. If you put this function in a destructor, the synchronous update that saves the implementation data of the update operation and the persistence of the data are called automatically each time the PHP code snippet finishes executing.  -  About--------------------------------------------------------------------------------------------------------------- ---------------------------- $             classtest{ -  -                  Public $db _url= ' localhost:3306 '; -                  Public $db _user= ' Root '; A                  Public $db _pwd= ' Root '; +  the                  Public function__construct () { -                     $link=mysql_connect($db _url,$db _user,$db _pwd);//Connect Database Operations $                 } the  the                  Public function__destruct () { the                     Mysql_close($link);//close this connection resource instead of destroying the object when the object is fired, the system automatically calls the destructor to execute the connection to close the resource.  the                 } -             } in              the             $dao=NewTest (); the             unset($dao); TipsThe object is actually destroyed when the object is unset, but the MySQL connection resource still exists and can execute the SQL statement About  the             $sql= "Show Databases"; the             $result=mysql_query($sql);//The result is a return value indicating that the resource connection persists after the object is destroyed the  +  ---------------------------------------------------------------------------------------------------------------- --------------------------- theTips: The destructor is not destroying the object itself, but is used to close the resource connection.

PHP's destructor study notes